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Bolt Weight Calculator | Professional Fastener Mass & Cost Estimator

Accurate bolt weight calculator for hex, socket, stud & more. Metric & imperial units. Includes nut, washer, coating, material library & total cost.
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The Bolt Weight Calculator is a professional-grade tool designed for engineers, fabricators, procurement teams, and field technicians to quickly and accurately estimate the mass of fasteners.

Whether you're working with standard hex bolts, heavy hex, socket head cap screws, carriage bolts, studs, or custom fasteners, this calculator handles both metric (mm/kg) and imperial (inch/lb) units. It accounts for:

  • Precise thread geometry (effective root diameter)
  • Head style and dimensions
  • Material density (steel, stainless, aluminum, titanium, brass, etc.)
  • Coating weight allowance
  • Optional nut and washer assembly
  • Quantity, packaging overhead, material cost, and freight estimation

Results include per-bolt weight, total lot weight, volume, detailed breakdown, sensitivity analysis, and export options (CSV/PDF). Built with real-world standards (ISO 4014, DIN, ASME B18.2.1), it delivers reliable theoretical estimates within ±5–10% accuracy — ideal for BOM preparation, shipping calculations, and cost planning.

Enter your bolt specifications and click Calculate Weight to get instant results.

Bolt Weight Calculator

Professional Fastener Mass Estimator — Metric & Imperial

✓ 90–95% Accuracy | ISO, DIN, ASME Standards
📐

Bolt Geometry & Type

Outer thread diameter

Tip to under-head

Hex width (A/F)

Metric pitch or 1/TPI

Leave 0 for full thread

🧱

Material & Grade

Edit for custom alloys

🔧

Assembly Options

📦

Quantity & Cost

Optional: for cost estimate

Optional: shipping cost per kg

✓ Data copied to clipboard!
Enter values and calculate
🔩

Fill in dimensions and hit Calculate Weight

📐 CALCULATION FORMULAS (LaTeX)

Effective Thread Root Diameter:

\[ d_{eff} = d - 1.2269 \times p \]

Unthreaded Shank Volume:

\[ V_{shank} = \pi \times \left(\frac{d}{2}\right)^2 \times L_{shank} \]

Threaded Portion Volume:

\[ V_{thread} = \pi \times \left(\frac{d_{eff}}{2}\right)^2 \times L_{thread} \]

Hex Head Volume (Hexagonal Prism):

\[ V_{head} = \frac{3\sqrt{3}}{2} \times \left(\frac{s}{2}\right)^2 \times k \]

Total Bolt Volume:

\[ V_{total} = V_{head} + V_{shank} + V_{thread} \]

Single Bolt Weight with Coating Factor:

\[ W_{bolt} = V_{total} \times \rho \times (1 + f_{coating}) \]

Total Lot Weight:

\[ W_{lot} = W_{bolt} \times Q \times (1 + f_{pkg}) \]

Nut Weight Approximation (Hex Nut):

\[ W_{nut} \approx \left(\frac{3\sqrt{3}}{2} \times \left(\frac{s}{2}\right)^2 - \pi \times \left(\frac{d}{2}\right)^2\right) \times h_{nut} \times \rho \]

Flat Washer Weight:

\[ W_{washer} = \pi \times \left(\left(\frac{D_{outer}}{2}\right)^2 - \left(\frac{D_{inner}}{2}\right)^2\right) \times t \times \rho \]

Where: d = nominal diameter, p = thread pitch, s = across-flats, k = head height, L = length, ρ = density, f = factor, Q = quantity

Adjust the slider to see how bolt weight varies with diameter or length. Run a calculation first.

12 mm
80 mm

Click a row to apply that density to your calculation.

MaterialGrade / TypeDensity (kg/m³)

Add multiple bolt types for a full Bill of Materials.

#TypeDiam.LengthMatl.QtyWt/pc (g)Total (kg)

🔩 Related Engineering Tools

Explore our complete fastener and structural engineering calculator suite.

⚙️ Nut Weight Calculator 🔘 Washer Weight Calculator 🏗 Steel Weight Calculator 💰 Fastener Cost Estimator 📦 Shipping Load Planner 📊 Structural Load Tool
Bolt Weight Calculator — Results are theoretical estimates ±5–10%. Always verify with physical measurement for precision applications. ISO 4014 | DIN 931 | ASME B18.2.1

Complete Reference Guide

Bolt Weight Calculator:
User Guide, Formulas & FAQ

A professional fastener mass estimator covering metric and imperial systems, material densities, and structural bolt weight calculations — ISO 4014 · DIN 931 · ASME B18.2.1

⚡ Step-by-Step 📐 All Formulas ✅ 90–95% Accuracy 🌍 Metric & Imperial 📦 BOM & CSV Export
Overview

What Is the Bolt Weight Calculator?

The Bolt Weight Calculator is a free, browser-based fastener mass estimator that calculates the weight of bolts, screws, studs, anchor bolts, and other threaded fasteners using their physical dimensions and material density. It supports both metric (mm/kg) and imperial (in/lb) unit systems, and covers standards including ISO 4014, DIN 931, and ASME B18.2.1.

Whether you are a structural engineer estimating bolt weight for a steel frame, a procurement specialist calculating shipping loads, or a manufacturer building a Bill of Materials (BOM), this bolt mass estimation tool eliminates the need for complex spreadsheets or manual formulas. It handles hex bolts, socket head cap screws, carriage bolts, stud bolts, anchor bolts, flange bolts, lag bolts, countersunk screws, eye bolts, and heavy hex bolts — with options for nut and washer weight calculation, coating factors, and batch quantity pricing.

📏
Accuracy Note (Read Before You Use):

This bolt weight calculation tool delivers 90–95% accuracy for standard fastener geometries. Results are theoretical estimates based on ideal geometric volumes. Real bolts have chamfers, fillet radii, and thread root geometry that reduce mass by approximately 5–10% compared to these calculations. For critical structural or metrology applications, always verify by weighing a physical sample. The tool is ideal for procurement planning, shipping load estimation, and engineering quotations.

Value Proposition

Key User Pain Points & How This Calculator Solves Them

😣 Pain Point
Problem: Manually calculating bolt weight in Excel is error-prone and requires knowing the exact formula for hex head volume, thread root diameter, and density conversions.

✅ Fix: The calculator applies ISO-standard formulas automatically. Enter your dimensions and hit Calculate — no spreadsheet required.

😣 Pain Point
Problem: Sourcing accurate material density values for stainless steel 316, titanium, brass, or Inconel is time-consuming and scattered across datasheets.

✅ Fix: The built-in material library includes 14 common bolt materials with verified density values (kg/m³), selectable with one click.

😣 Pain Point
Problem: Calculating total shipping weight for a mixed fastener order (bolts + nuts + washers) across hundreds or thousands of pieces is tedious.

✅ Fix: The BOM (Bill of Materials) tab lets you add multiple bolt types, compute all weights simultaneously, and export a CSV for your freight or purchasing team.

😣 Pain Point
Problem: Converting between metric bolt weight (kg) and imperial (lb/oz) mid-project causes confusion and unit errors.

✅ Fix: The unit toggle instantly switches all inputs and outputs between metric and imperial, with no recalculation needed.

😣 Pain Point
Problem: Hot-dip galvanized or PTFE-coated bolts weigh more than bare fasteners — a factor often ignored in procurement estimates.

✅ Fix: Select a coating type (zinc, HDG, nickel, PTFE, etc.) and the calculator automatically applies the correct mass factor to your result.

😣 Pain Point
Problem: Engineers need PDF documentation of bolt weight calculations for project records and client submissions.

✅ Fix: The PDF Report export generates a print-ready document showing all input parameters, volumes, weights, and formulas used.

Visual Reference

Bolt Anatomy & Key Dimensions Diagram

Understanding the physical parts of a bolt is essential for accurate fastener weight calculation. The diagram below shows the key dimensions used in every calculation this tool performs.

BOLT ANATOMY — KEY DIMENSIONS FOR WEIGHT CALCULATION d (nominal dia) L (total length, tip to under-head) k (head height) s (A/F) Lt (threaded length) HEX HEAD UNTHREADED SHANK THREADED PORTION TIP

Figure 1: Bolt anatomy showing all key dimensions used in weight calculation. Dimensions: d = nominal diameter, L = total bolt length, k = head height, s = across-flats (A/F), Lt = threaded length, p = thread pitch (not shown — see formula section).

Field Reference

Input Reference: All Fields, Units & Accepted Ranges

Use this table as a quick reference for every input field in the bolt weight estimation tool. Entering values outside the valid ranges will produce unrealistic results.

Field / Symbol Description Metric Unit Imperial Unit Typical Range Common Mistake
d — Nominal Diameter Outer thread diameter. The number in a bolt's name (e.g., "M12" → d = 12 mm). mm in 1 – 300 mm Entering the thread root diameter instead of nominal diameter
L — Total Length Measured from the tip of the bolt to the underside of the head. Does NOT include head height. mm in 5 – 3000 mm Including head height in the length measurement
s — Across Flats (A/F) The width of the hex head measured across parallel flat faces. Found on bolt specifications. mm in 5 – 300 mm Using "across corners" dimension instead of "across flats"
k — Head Height Vertical height of the bolt head only. Varies by head style (hex, socket, flange, etc.). mm in 1 – 100 mm Leaving at default when using a non-standard or heavy hex head
p — Thread Pitch For metric: distance between threads in mm. For imperial UNC/UNF: enter 1/TPI (e.g., 1/13 = 0.077"). mm in 0.1 – 10 mm Entering TPI directly instead of 1/TPI for imperial bolts
Lt — Threaded Length Length of the portion of shank with threads. Enter 0 for fully-threaded bolts (studs). mm in 0 – L Setting to 0 for partially-threaded bolts (makes calculator assume full thread)
ρ — Material Density Density of the bolt material in kg/m³. Auto-populated when you select a material from the dropdown. kg/m³ kg/m³ 1000 – 22000 Using density in g/cm³ (must multiply by 1000 to convert to kg/m³)
Coating Factor Percentage mass added by surface coatings. Hot-dip galvanizing adds ~5%; zinc electroplate adds ~2%. % % 0 – 10% Ignoring coating weight on HDG structural bolts (can add significant mass)
Quantity Number of bolts for total lot weight and cost calculation. pcs pcs 1 – 10,000,000 Forgetting to update quantity before exporting total weight for shipping
How to Use

Step-by-Step Guide: How to Calculate Bolt Weight

Follow these steps in order to get accurate bolt mass estimates for any fastener type, material, and quantity.

  1. Select Your Unit System

    At the top of the calculator, toggle between Metric (mm/kg) and Imperial (in/lb). All input fields and output results will update labels automatically. The underlying calculation always uses SI units internally, then converts for display.
    ⚠ Tip: Choose your unit system FIRST before entering any values to avoid confusion.

  2. Choose a Bolt Type & Head Style

    Select from 10 bolt types: Hex Bolt, Heavy Hex, Socket Head Cap Screw, Countersunk, Carriage Bolt, Stud Bolt, Anchor Bolt, Eye Bolt, Flange Bolt, or Lag Bolt/Screw. The head style dropdown will auto-select the correct default for your chosen type, but you can override it.
    ⚠ Tip: Stud bolts have no head — the calculator still uses head dimensions for the formula; set head height (k) to 0 for a pure stud calculation.

  3. Load a Standard or Enter Custom Dimensions

    Use the Standard dropdown to auto-fill dimensions for ISO standard bolts (M6 through M36) or ASME sizes (1/2" through 1"). For custom bolts, leave it on "Custom / Manual" and enter your measured values for:
    • Nominal Diameter (d) — the thread outer diameter
    • Total Length (L) — tip to under-head
    • Across Flats (s) — hex head A/F width
    • Head Height (k) — height of head
    • Thread Pitch (p) — distance between threads
    • Threaded Length (Lt) — 0 for full thread
    ⚠ Tip: For M12 bolts, use the ISO standard loader to avoid manual entry errors.

  4. Select Material & Grade

    Pick a material from the dropdown (14 options including carbon steel, stainless steel 304/316, brass, aluminum, titanium, Inconel, and more). The density field auto-fills with the correct value in kg/m³. For alloys not in the list, select "Custom Density" and type in your value. Also select the bolt grade (4.6 to 12.9, A193 B7, A325, A490, SAE Grade 5/8) and coating type.
    ⚠ Tip: Density for Stainless 304 is 8000 kg/m³, not 7850. Using the steel default underestimates SS bolt weight by ~2%.

  5. Add Nut & Washer Weight (Optional)

    Check "Include Nut Weight" and/or "Include Washer Weight" to add the fastener assembly mass. Select nut type (standard hex, heavy hex, nyloc, flange) and washer type (flat, spring, Nord-Lock, fender) and specify quantity per bolt. The same material density as the bolt is applied.
    ⚠ Tip: For shipped assemblies (bolt + nut + 2 washers), always enable all three to get accurate gross weight for freight calculations.

  6. Enter Quantity, Price & Freight Rate

    Enter the number of bolts (pieces). Optionally enter a price per kg for material cost estimation and a freight rate per kg for shipping cost. Check "Add 5% packaging overhead" to account for crates, boxes, and dunnage weight.
    ⚠ Tip: Price per kg is for the fastener material cost, not the per-piece purchase price. Convert your supplier pricing before entering.

  7. Click "⚡ Calculate Weight"

    Press the orange Calculate button (or press Enter from any input field). Results appear instantly in the Results tab showing: weight per bolt (g or oz), total lot weight (kg or lb), weight per 100 pieces, and volume per bolt (cm³). A bolt dimension diagram is also rendered showing your exact proportions.

  8. Review Breakdown & Explore Tabs

    The Results tab shows a detailed Weight Breakdown table splitting head, shank, threaded portion, nuts, and washers. Switch to:
    • Formulas tab — view all LaTeX equations and the calculation trace for your inputs
    • Chart tab — sensitivity analysis showing weight vs. diameter
    • Materials tab — click any material row to apply its density
    • BOM tab — build a multi-line Bill of Materials

  9. Export: CSV, PDF Report, or Copy to Clipboard

    Use the export buttons in the Results tab to download a CSV file (opens in Excel) with all parameters and results, generate a PDF Report (print-ready with formulas and all computed values), or copy everything to clipboard for pasting into emails or documents. The BOM tab also has its own CSV export.
    ⚠ Tip: The PDF export opens in a new browser tab and triggers the print dialog — save as PDF using your browser's print-to-PDF option.

Engineering Mathematics

All Bolt Weight Calculation Formulas Explained

The calculator uses geometric volume formulas for each bolt component, multiplied by material density. Here is a complete explanation of every formula used in the bolt mass estimation process.

① Thread Root Diameter (deff)

d_eff = d − 1.2269 × p

The effective (root) diameter of the threaded section. Uses the ISO metric thread standard reduction factor (1.2269) applied to thread pitch p. This ensures the threaded portion's volume is correctly reduced from the nominal diameter. Unit: mm.

② Unthreaded Shank Volume (Vshank)

V_shank = π × (d/2)² × L_shank

The shank is a simple cylinder of diameter d and length L_shank = L − L_thread. Uses the full nominal diameter since the shank has no thread reduction. Unit: mm³.

③ Threaded Portion Volume (Vthread)

V_thread = π × (d_eff/2)² × L_thread

Uses the reduced thread root diameter d_eff calculated above. The thread void between root and crest is thus accounted for. For fully-threaded bolts (studs), L_thread = L and L_shank = 0. Unit: mm³.

④ Hex Head Volume (Vhead)

V_head = (3√3/2) × (s/2)² × k

Models the hex head as a regular hexagonal prism. The area of a regular hexagon with "across-flats" width s is (3√3/2)×(s/2)². Multiplied by head height k to get volume. Unit: mm³. For socket heads: π×(s/2)²×k. For flat/countersunk: approximated as truncated cone.

⑤ Total Bolt Volume (Vtotal)

V_total = V_head + V_shank + V_thread

Simple sum of all three geometric components. Expressed in mm³, then converted to cm³ (÷1000) for display. This total volume is the basis for all weight calculations that follow.

⑥ Single Bolt Weight (Wbolt)

W_bolt = V_total × 1e-6 × ρ × 1000 × (1 + f_coat)

Converts volume from mm³ to m³ (×10⁻⁶), multiplies by density ρ in kg/m³ to get kg, then converts to grams (×1000). The coating factor f_coat adds mass as a percentage (e.g., 0.05 for +5% hot-dip galvanizing). Unit: grams.

⑦ Hex Nut Weight (Wnut)

W_nut = [(3√3/2)×(s/2)² − π×(d/2)²] × h_nut × ρ × 1e-6 × 1000

The nut is a hexagonal prism with a cylindrical hole (thread bore). The net cross-sectional area is the hex area minus the bolt hole area. Nut height h_nut ≈ 0.8×d by approximation. Multiplied by density and unit conversion. Unit: grams.

⑧ Flat Washer Weight (Wwasher)

W_wash = π × [(OD/2)² − (ID/2)²] × t × ρ × 1e-6 × 1000

A flat washer is a hollow cylinder (annular disc). The calculator uses standard proportions: OD ≈ 2.2×d, ID ≈ d + 0.5 mm, thickness t ≈ 0.15×d. The annular cross-sectional area (OD ring minus ID hole) multiplied by thickness gives the volume. Unit: grams.

⑨ Total Lot Weight Formula (All Pieces Combined)

W_lot = (W_bolt + W_nut + W_washer) × Quantity × (1 + f_packaging) ÷ 1000

Sums the complete assembly weight (bolt + optional nut + optional washer) per piece, multiplies by quantity, adds packaging overhead (5% if selected), and converts grams to kilograms. This is the final shipping/procurement weight in kg (or lb in imperial mode).

Variable Legend

SymbolMeaningUnit
dNominal bolt diameter (outer thread)mm
d_effThread root (effective) diametermm
pThread pitch (metric) or 1/TPI (imperial)mm
sAcross-flats hex width (A/F)mm
kHead heightmm
LTotal bolt length (tip to under-head)mm
L_shankUnthreaded shank length = L − L_threadmm
L_threadThreaded lengthmm
ρ (rho)Material densitykg/m³
f_coatCoating mass factor (0.02–0.07)dimensionless
f_pkgPackaging overhead factor (0 or 0.05)dimensionless
QQuantity of boltspieces
1e-6Unit conversion: mm³ → m³—
Practical Example

Worked Example: M12 × 80mm Grade 8.8 Carbon Steel Hex Bolt

This example walks through the complete steel bolt weight calculation step by step for a common structural bolt — M12 × 80mm, Grade 8.8, ISO 4014 standard, with 32mm of threading.

📋 Given Inputs

d12 mm (nominal diameter)
L80 mm (total length, tip to under-head)
s (A/F)18 mm (across flats, ISO 4014)
k7.5 mm (head height, ISO 4014)
p1.75 mm (M12 coarse thread pitch)
Lt32 mm (threaded length → L_shank = 80 − 32 = 48 mm)
ρ7850 kg/m³ (carbon steel)
d_eff = 12 − 1.2269 × 1.75 = 9.853 mm V_shank = π × (12/2)² × 48 = π × 36 × 48 = 5,428.7 mm³ V_thread = π × (9.853/2)² × 32 = π × 24.27 × 32 = 2,441.0 mm³ V_head = (3√3/2) × (18/2)² × 7.5 = 2.598 × 81 × 7.5 = 1,578.2 mm³ V_total = 5428.7 + 2441.0 + 1578.2 = 9,447.9 mm³ ≈ 9.448 cm³ W_bolt = 9447.9 × 10⁻⁶ × 7850 × 1000 × (1 + 0) = 74.17 g per bolt Lot weight (Q=100, no pkg): W_lot = 74.17 × 100 ÷ 1000 = 7.417 kg
💡
Comparison to real weight:

A weighed M12×80 Grade 8.8 hex bolt typically measures 65–70 grams in practice. Our calculated 74.2 g is ~6% higher — consistent with the stated ±5–10% estimate range. The difference comes from thread root geometry, chamfers, and fillet radii that remove material from the idealized geometric model.

Material Reference

Fastener Material Density Reference Table

The bolt density calculation is the most critical variable in fastener weight estimation. Using the wrong density value — for example, applying carbon steel density to a stainless steel 316 bolt — can cause a 2–4% error per bolt, compounding significantly over large quantities. Use this verified reference table:

Material Grade / Standard Density (kg/m³) Typical Bolt Applications Weight vs Steel
Mild / Carbon Steel ASTM A307 / 4.6 7,850 General structural, construction, machinery Baseline (100%)
Alloy Steel Grade 8.8 / 10.9 7,900 High-strength structural, automotive, machinery +0.6%
Stainless Steel 304 A2-70 8,000 Food processing, outdoor, marine (moderate) +1.9%
Stainless Steel 316 A4-80 8,030 Marine, chemical, high-corrosion environments +2.3%
Brass CW614N 8,500 Electrical, plumbing, low-load decorative +8.3%
Aluminum 6061-T6 2,700 Aerospace, automotive lightweight, electronics −65.6% (lightest common metal)
Titanium Grade 5 Ti-6Al-4V 4,510 Aerospace, medical implants, racing −42.5%
Inconel 718 N07718 8,442 Jet engines, gas turbines, high-temperature +7.5%
Copper C110 8,920 Electrical grounding, heat exchangers +13.6%
Bronze C932 8,770 Marine hardware, bearing applications +11.7%
Nylon / PA6 PA6 1,150 Electrical insulation, low-load plastic applications −85.4% (lightest option)
Monel 400 N04400 8,800 Marine, chemical processing, offshore +12.1%
Microcopy & Tips

Common Bolt Weight Calculation Mistakes & How to Avoid Them

  • 📏
    Measuring Length Including the Head

    The bolt length (L) in fastener standards is always measured from the tip to the underside of the head — the head is separate. If you include the head in L, you will double-count it in the volume calculation. ✓ FIX: Measure from under-head only

  • 📐
    Using "Across Corners" Instead of "Across Flats"

    A hex head has two different measurements: across flats (the smaller, A/F value you use for a wrench) and across corners (the larger, diagonal value). The calculator requires "across flats" (s). Using across corners inflates head volume by up to 15%. ✓ FIX: Use the wrench/spanner size

  • 🔢
    Entering TPI Instead of Pitch for Imperial Bolts

    For imperial bolts, thread is specified in TPI (Threads Per Inch). The pitch field expects the pitch in inches = 1 ÷ TPI. A 1/2"-13 UNC bolt has a pitch of 1/13 = 0.0769 inches, not "13". ✓ FIX: Enter 1/TPI (e.g., 0.077)

  • 🧱
    Using Carbon Steel Density for Stainless Steel Bolts

    Carbon steel (7850 kg/m³) and stainless steel 316 (8030 kg/m³) differ by ~2.3%. For a large structural project with 10,000 SS bolts, this error alone can misstate weight by 15–20 kg. ✓ FIX: Select SS304 or SS316 from the material dropdown

  • 🪙
    Ignoring Coating Weight for Hot-Dip Galvanized Bolts

    Hot-dip galvanizing (HDG) adds approximately 5–7% to a bolt's mass due to the thick zinc coating. For a 1-tonne lot of structural anchor bolts, ignoring this factor understates weight by 50–70 kg. ✓ FIX: Select "Hot-Dip Galvanized (+5%)" in the coating dropdown

  • 🔩
    Forgetting to Set Threaded Length = 0 for Stud Bolts

    Stud bolts and threaded rods are fully threaded (no shank). If you leave the threaded length (Lt) field at a partial value like 32mm, the calculator will model an unthreaded shank, increasing calculated volume (and weight) incorrectly. ✓ FIX: Enter 0 in the Threaded Length field for studs

Frequently Asked Questions

Bolt Weight Calculator FAQ

How accurate is this bolt weight calculator? +
The calculator delivers 90–95% accuracy for standard ISO/ASME hex bolts. The remaining 5–10% error comes from physical features not modeled: thread root geometry (the theoretical reduction factor 1.2269 is an approximation), head chamfers and fillets, tip chamfers, and manufacturing tolerances. For procurement and logistics planning this accuracy is excellent. For exact metrology or material testing, weigh a physical sample. The tool uses the same geometric formulas as engineering handbooks and Excel weight calculators used by fastener manufacturers.
How do I calculate bolt weight in kg for a large structural order? +
Enter your bolt dimensions and material, then set the Quantity field to your total piece count. The "Total Weight" result card will show the combined weight in kg. For mixed fastener orders (multiple bolt sizes or types), use the BOM tab to add multiple rows, compute all at once, and export a full Bill of Materials CSV. Don't forget to include nut and washer weight if your order includes assembled sets, and enable the "5% packaging overhead" option for gross weight freight calculations.
Can I use this as a metric bolt weight calculator for M-series bolts? +
Yes. The Standard dropdown includes pre-loaded dimensions for M6, M8, M10, M12, M16, M20, M24, M30, and M36 bolts per ISO 4014. Selecting a standard auto-fills the diameter, across-flats, head height, thread pitch, and threaded length fields with ISO-standard values. You can then adjust the length field to match your specific bolt length. Make sure the unit toggle is set to Metric (mm/kg) for correct results.
How do I calculate anchor bolt weight? +
Select Anchor Bolt from the Bolt Type dropdown. Anchor bolts are typically partially or fully threaded rods with a head, hook, or L-bend at one end. For an L-bolt or J-bolt, use the Stud Bolt type with Threaded Length = 0 (fully threaded) for the best approximation, since the bend portion has the same cross-section as the shank. The head volume section models the anchor plate if present. For hex-head anchor bolts embedded in concrete, use the Hex Bolt type and enter the full embedded length as L.
Can I calculate stud bolt weight (threaded rod) with this tool? +
Yes. Select Stud Bolt (Threaded Rod) from the bolt type dropdown. In the Threaded Length field, enter 0 to tell the calculator the entire length is threaded (no unthreaded shank). The head volume will still be included in the calculation — if the stud has no head at all, you can workaround this by setting head height (k) to a very small value like 0.1 mm to effectively eliminate the head contribution. The formula will then compute the full-length threaded rod mass.
Does the calculator work for nut weight calculation too? +
Yes. In the Assembly Options card, check "Include Nut Weight." You can select the nut type (standard hex, heavy hex, nyloc, or flange nut) and enter how many nuts per bolt. The nut is modeled as a hex prism with a cylindrical through-hole, with height approximated at 0.8×d. The same material density as the bolt is applied. Nut weight is shown separately in the breakdown table, and is included in the total assembly weight and lot weight calculations.
How do I export bolt weight calculation results to Excel or PDF? +
After calculating, three export options are available in the Results tab: ⬇ CSV Export downloads a comma-separated file that opens directly in Microsoft Excel or Google Sheets with all parameters and results; 🖨 PDF Report opens a formatted print-ready page in a new browser tab — use Ctrl+P (or Cmd+P on Mac) and select "Save as PDF" from the printer dropdown to download it; 📋 Copy All copies a plain-text summary to your clipboard for pasting into emails, quotes, or reports. The BOM tab has its own CSV export for multi-bolt lists.
What is the weight-to-diameter ratio for common bolts? +
The weight-to-diameter relationship is non-linear — weight scales with the square of diameter (from the circular cross-section). Approximate weights for standard carbon steel hex bolts of 80mm length: M6 ≈ 7–8g, M8 ≈ 15g, M10 ≈ 25–28g, M12 ≈ 45–50g, M16 ≈ 100–110g, M20 ≈ 190–210g, M24 ≈ 350–380g. Use the Chart tab's sensitivity slider in the calculator to visualize how weight changes with diameter at your specific length and material.
Can I use this as an online bolt weight calculator without downloading anything? +
Yes — the calculator runs entirely in your browser with no installation, login, or download required. All calculations are performed locally in JavaScript; no data is sent to any server. It is mobile-optimized and touch-friendly, making it suitable for field use on smartphones and tablets. It works on Chrome, Firefox, Safari, and Edge. For offline use, you can save the page using your browser's "Save Page As" function, though internet access is required for MathJax LaTeX formula rendering in the Formulas tab.
Why does my calculated weight differ from the bolt manufacturer's catalog weight? +
Manufacturer catalog weights are typically measured from physical samples and include all geometric features: head chamfers, thread run-out zones, fillet radii at the shank-to-head transition, and tip chamfers — all of which remove material that our idealized geometric model includes. This is why real bolts typically weigh 5–10% less than calculated theoretical values. Additionally, some manufacturers weigh bolts in full-thread-engagement assemblies or with specific coating thicknesses that differ from the calculator's approximations. Our results are intentionally slightly conservative (heavier) for safety margin in structural weight budgeting.