Cold-Formed Steel Design Calculator
Cold-Formed Steel (CFS) Design Calculator
Size and check light-gauge steel studs, tracks, headers, and connections — section properties, axial & flexural capacity, web crippling, and screw connections, per AISI S100 or AS/NZS 4600.
Section geometry
Formulas used (thin-wall centerline method)
Section & material
Tip: calculate a section in Tab 1, then re-enter its Ag / Ix / Sx / rx / ry here — or overwrite with your own catalog values.
Bracing & unbraced lengths
Applied loads (demand)
Axial capacity — Direct Strength Method (simplified)
Flexural & shear capacity
Combined axial + bending (AISI H1.2, simplified)
Web crippling / bearing check
Formula — AISI S100 Section G (single unstiffened web)
Screw connection capacity
Formulas — AISI S100 Section E4 (approximate)
Project info
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User Guide: Cold-Formed Steel Design Calculator
Cold-formed steel (CFS) members look simple, but the math behind sizing a stud, checking a header, or verifying a screw connection pulls together section geometry, buckling theory, and code equations from AISI S100 or AS/NZS 4600. This guide walks through every formula used inside the SteelSolver CFS Calculator — with worked numbers, unit callouts, common mistakes, and answers to the questions engineers ask most.
How to Use the Cold-Formed Steel Calculator: Step-by-Step Guide
The calculator is organized into five tabs that mirror a real CFS design workflow: geometry first, then member capacity, then the two checks engineers most often forget — bearing and connections.
1Set units, design code, material grade
Pick Imperial (in, ksi, kip) or Metric (mm, MPa, kN), your design code (AISI S100 or AS/NZS 4600), your design method (LRFD or ASD), and a yield strength grade. Switching units updates every input label in real time so you're never guessing whether a field wants inches or millimeters.
Common mistake: changing the unit toggle does not convert numbers already typed into the boxes — it only relabels the fields. Re-enter values in the new unit system, or finish a full calculation before switching.
2Calculate section properties
Choose a shape (lipped C-stud, unlipped track/U-channel, or hat section), enter web depth, flange width, lip length, thickness, and inside bend radius, then press Calculate section properties. You'll get gross area (Ag), moment of inertia (Ix), section modulus (Sx), radius of gyration (rx), and an estimated weight per length — plus a one-click button that carries these numbers straight into the Member Design tab.
3Run member design checks (axial, flexural, shear)
Enter bracing lengths (KxLx, KyLy), the compression flange width, and your applied loads (Pu, Mu, Vu). The calculator returns nominal and design capacities for axial compression, bending, and shear, plus a combined P-M utilization ratio — each with a color-coded pass/fail status and a percentage bar.
Reading the utilization ratio: what the colors mean
Every check in the calculator — axial, flexural, shear, combined, web crippling, and screw connection — reports its result as a utilization ratio (demand ÷ design capacity), color-coded the same way throughout the tool:
Green means the member has comfortable reserve capacity. Amber means it technically passes but is close enough to the limit that a small load increase could push it over. Red means demand exceeds design capacity — resize the section, add bracing, or add a stiffener/fastener before moving forward.
4Check web crippling at bearing points
Select the loading condition (end or interior reaction, one or two flanges loaded), enter web thickness, yield strength, flat web height, bend radius, and bearing length, then compare the applied reaction against the calculated capacity.
5Verify screw connection capacity
Pick a screw size, enter the thinner and thicker sheet properties, washer/head diameter, and screw count, and the tool checks shear/bearing, pull-out, and pull-over — reporting whichever governs.
6Build and export your report
Add a project name, engineer, date, and member ID, then click Build report to assemble every result into one plain-text summary — copy it to your clipboard or use your browser's print dialog to save it as a PDF for the project file.
Section Property Formulas for Cold-Formed Steel Members (Centerline Method)
Every capacity check downstream depends on getting the section geometry right first. The calculator uses the thin-wall centerline method — a standard simplification used throughout cold-formed steel design where each flat element (web, flange, lip) is treated as a straight line segment at mid-thickness.
Figure 1 — Lipped C-section (stud) with the four inputs the calculator needs: web depth d, flange width b, lip length c, and thickness t (plus inside bend radius R).
The section property formulas
What this calculation is used for
Section properties feed every other module: Ag drives axial capacity, Ix/Sx drive bending capacity and deflection, and rx/ry drive slenderness and buckling checks. Get this step wrong and every downstream utilization ratio is wrong too.
Where engineers apply it
Sizing a custom or non-catalog CFS shape, verifying a manufacturer's published properties, or building a quick model of a built-up (back-to-back or boxed) section before a formal submittal.
Common mistakes
- Entering the out-to-out depth or width instead of a centerline (flat) dimension — this tool works in flat/centerline lengths and neglects corner-radius effects for simplicity, which shifts results slightly versus a full corner-corrected calculation.
- Forgetting that lip length is measured from the flange face, not the overall stud depth.
- Mixing mil/gauge thickness with decimal inches — 54 mil is 0.0538 in, not 0.54 in.
Axial Capacity Formulas: Direct Strength Method (DSM) Buckling Checks
Thin-walled CFS columns rarely fail by simple yielding — they buckle first, in one of three ways. The Direct Strength Method (DSM) in AISI S100 checks all three and takes the lowest capacity as governing.
Global (flexural) buckling
Local buckling
Distortional buckling
Governing axial capacity
What this calculation is used for
Sizing load-bearing studs, king/jack studs at openings, and any axially-loaded CFS compression member — the governing mode tells you why a section fails, which points to the fix (brace it tighter for global buckling, thicken the flange for local buckling, or add a bigger lip/stiffener for distortional buckling).
Where engineers apply it
Load-bearing wall stud design, king studs supporting headers, axially-loaded jamb studs at window and door openings, and preliminary column checks for light-gauge braced frames.
Common mistakes
- Using the unbraced physical length instead of the effective length KL — bridging and blocking change the effective length independently in each axis.
- Forgetting that weak-axis (KyLy/ry) almost always governs slenderness for a stud, since ry is much smaller than rx.
- Reading "Pn" as the safe working load directly — always apply the design factor (φ or Ω) before comparing against demand.
Flexural and Shear Capacity Formulas for CFS Members
Bending (flexural) capacity
Shear capacity
What this calculation is used for
Header and joist design where bending moment or end-reaction shear governs, rather than axial load — most floor joists, roof rafters, and lintels/headers are flexural members first.
Where engineers apply it
CFS joists and headers spanning openings, curtain-wall mullions under wind load, and any horizontal member checked for moment, shear, and deflection together.
Common mistakes
- Using the gross section modulus (Sx) as the final answer without any local-buckling reduction — thin, wide compression flanges rarely reach full yield before buckling.
- Checking bending and shear at the same location when they typically govern at different points along the span (moment at midspan, shear at supports).
Combined Axial + Bending Interaction Check
What this calculation is used for
Studs that carry both axial load from the floor/roof above and out-of-plane bending from wind or seismic pressure on the wall — almost every exterior load-bearing stud falls into this category.
Common mistakes
- Checking axial and bending in isolation and missing that a section passing both individually can still fail the combined check.
Web Crippling Formula for Cold-Formed Steel (AISI S100 Section G)
Web crippling — local yielding/buckling of the thin web directly under a concentrated load or reaction — is one of the most commonly skipped CFS checks, yet it governs surprisingly often at bearing points.
| Condition | C | Cₑ | Cₙ | Cℎ |
|---|---|---|---|---|
| End reaction, one flange loaded | 4.0 | 0.14 | 0.35 | 0.02 |
| Interior reaction, one flange loaded | 13.0 | 0.23 | 0.14 | 0.01 |
| End reaction, two flanges loaded | 7.5 | 0.08 | 0.79 | 0.12 |
| Interior reaction, two flanges loaded | 20.0 | 0.10 | 0.28 | 0.01 |
Design factors: LRFD φ = 0.85, ASD Ω = 1.75.
What this calculation is used for
Checking whether a stud or joist web needs a bearing stiffener at a support, end condition, or point load — very common at header ends, joist-over-beam bearing, and track-to-stud reactions.
Where engineers apply it
Joist bearing on a ledger or beam, stud reactions into track, and any location where a concentrated load bears directly onto an unstiffened, thin web.
Common mistakes
- Forgetting this check entirely — web crippling is a bearing/local check, not covered by the axial or flexural capacity calculations above.
- Using validity ranges outside the tabulated limits (h/t ≤ 200, N/t ≤ 210, R/t ≤ 6 for this coefficient set) without flagging the result as approximate.
- Applying single-web coefficients to a box or back-to-back built-up section, which needs a different, multi-web equation set.
Real-world usage: this check is exactly why manufacturers publish a minimum bearing length (commonly 1.5 in / 38 mm) and recommend bearing stiffeners at header ends — both directly change N and, through the stiffener, the effective web condition in this formula.
Screw Connection Capacity Formulas (AISI S100 Section E4)
Self-drilling screw connections can fail three different ways, and the calculator checks all three, reporting whichever governs.
What this calculation is used for
Attaching sheathing, track, clips, and built-up members (box headers, back-to-back studs) with self-drilling screws — the governing failure mode tells you whether to add more screws, use a bigger screw, or switch to a thicker/stronger sheet.
Where engineers apply it
Box-header ply-to-ply screw patterns, stud-to-track connections, sheathing attachment, and clip/bracket fastening schedules.
Common mistakes
- Mixing up t₁ and t₂ — the thinner/thicker sheet assignment changes which term governs.
- Ignoring minimum edge distance (typically 1.5d) and spacing (typically 3d) — this calculator checks connection strength only, not geometric minimums.
- Assuming pull-out or pull-over never governs — for thin sheets and small washers, they frequently do, as the worked example below shows.
Full Worked Example: Sizing a 600S162-54 Load-Bearing Stud
These numbers match the calculator's default inputs, so you can open the tool and reproduce every result below.
Section & member inputs
| Input | Value |
|---|---|
| Depth d / Flange b / Lip c / Thickness t | 6.000 in / 1.625 in / 0.500 in / 0.0538 in |
| Fy | 50 ksi |
| KxLx / KyLy | 96 in / 48 in |
| Ag / Ix / Sx / rx / ry | 0.667 in² / 4.40 in⁴ / 1.47 in³ / 2.57 in / 0.55 in |
| Applied loads Pu / Mu / Vu | 3.0 kip / 12.0 kip-in / 1.0 kip |
Axial capacity result
Governing slenderness is the weak axis: KyLy/ry = 48/0.55 = 87.3. That gives Fₑ ≈ 38.2 ksi, λᱮ ≈ 1.14, Fₙ ≈ 28.9 ksi, and Pₙₑ ≈ 19.3 kip. Local buckling doesn't reduce this (λℓ ≈ 0.69 is below the 0.776 threshold), and distortional buckling gives a higher 27.3 kip — so the section is governed by global (flexural) buckling at Pₙ ≈ 19.3 kip.
LRFD design capacity: φPₙ = 0.85 × 19.3 = 16.4 kip. Utilization = 3.0 / 16.4 = 0.18 — PASS
Flexural & shear results
Sₑ ≈ 0.9 × 1.47 = 1.32 in³, so Mₙ = 1.32 × 50 ≈ 66.2 kip-in. φMₙ = 0.90 × 66.2 ≈ 59.5 kip-in. Utilization = 12 / 59.5 = 0.20 — PASS. For shear, using h = 5.7 in: Aₖ = 0.307 in², Vₙ = 0.307 × 30 ≈ 9.2 kip, φVₙ ≈ 7.8 kip. Utilization = 1.0 / 7.8 = 0.13 — PASS.
Web crippling result — a governing FAIL case
Using end-reaction, one-flange-loaded coefficients with R = 0.075 in, N = 1.5 in, h = 5.7 in, and an applied reaction of 1.2 kip: Pₙ ≈ 1.09 kip, so φPₙ = 0.85 × 1.09 ≈ 0.93 kip. Utilization = 1.2 / 0.93 ≈ 1.29 — FAIL.
What this teaches: a stud can pass axial, flexural, and shear checks comfortably and still fail at its bearing point. The fix is usually one of: add a bearing stiffener, increase the bearing length N, or step up to a thicker gauge locally.
Screw connection result — where method choice matters
For a #10 screw (d = 0.190 in) through a 0.0538 in stud into an 0.0179 in track, with Fu1 = 45 ksi, Fu2 = 65 ksi, dₔ = 0.34 in, 4 screws, and Vu = 0.8 kip: pull-over governs at Pₙ ≈ 0.41 kip/screw.
LRFD: 4 × 0.50 × 0.41 ≈ 0.82 kip total. Utilization = 0.8 / 0.82 ≈ 0.97 — PASS (near limit).
ASD: 4 × (0.41/3.00) ≈ 0.55 kip total. Utilization = 0.8 / 0.55 ≈ 1.46 — FAIL.
Common mistake: assuming LRFD and ASD always agree on pass/fail for the same nominal loads — they don't, because the load factors baked into Pu/Mu/Vu and the resistance factors are calibrated together, not independently swappable mid-calculation.
Key User Pain Points and How This Calculator Solves Them
Manual DSM calculations are slow and error-prone
Hand-checking local, distortional, and global buckling for every trial section eats up design time.
How this tool helps: all three buckling modes calculate instantly and side-by-side, with the governing mode labeled.
Manufacturer tables don't match your exact conditions
Catalog span tables assume standard bracing and loading — not your project's actual spacing, holes, or load combination.
How this tool helps: enter your project's real geometry, bracing, and loads instead of interpolating between table rows.
Web crippling gets forgotten
Bearing/crippling checks are easy to skip when focused on axial and bending capacity.
How this tool helps: a dedicated tab makes the check a deliberate step, not an afterthought.
Switching between LRFD and ASD is confusing
Different φ and Ω factors for every limit state make it easy to mix methods by mistake.
How this tool helps: one global method toggle applies the correct factor to every check consistently.
No easy way to document a quick calculation
A one-off preliminary check often has nowhere to live for the project file.
How this tool helps: the Report tab builds a copy-ready summary and supports print-to-PDF.
Imperial/metric mix-ups
US catalogs are Imperial; AS/NZS and Eurocode projects are metric — switching mid-project causes unit errors.
How this tool helps: every field label updates instantly when you toggle units.
Common Mistakes to Avoid (Quick Reference)
- Mixing mil and inch thickness: 54 mil = 0.0538 in, not 0.54 in — a 10× error that silently wrecks every result.
- Using physical length instead of effective length KL: bracing and end conditions change KL independently in each axis.
- Skipping web crippling: it's a separate bearing check, not covered by axial/flexural capacity.
- Reading nominal capacity (Pₙ, Mₙ, Vₙ) as the safe design value: always apply φ (LRFD) or divide by Ω (ASD) first.
- Assuming LRFD and ASD give the same pass/fail: they can diverge, especially near a 1.0 utilization ratio.
A note on accuracy
This calculator uses documented, industry-standard equation forms (AISI S100 Direct Strength Method, Section G web crippling, Section E4 screw connections) with simplified, closed-form estimates in place of the finite-strip elastic buckling analysis a full DSM design normally requires. Every formula on this page is the exact equation implemented in the tool — nothing is hidden. Inputs are validated for positive, non-zero values before a calculation runs. For construction documents, permit submittals, or final structural design, verify results with dedicated finite-strip software (e.g. CUFSM) and have the design reviewed and stamped by a licensed engineer in your jurisdiction.
Frequently Asked Questions About Cold-Formed Steel Design Calculations
Is this calculator a replacement for AISI S100 finite-strip (CUFSM) software?
No. It uses simplified closed-form approximations for local and distortional buckling instead of a true finite-strip eigenvalue analysis. Treat results as a fast preliminary check, and confirm governing members with dedicated software before finalizing a design.
What's the difference between AISI S100 and AS/NZS 4600?
AISI S100 is the North American cold-formed steel specification; AS/NZS 4600 is the Australian/New Zealand equivalent. Both are built on similar Direct Strength Method principles but differ in load combination factors, some coefficients, and adopted editions — select the one matching your project's governing building code.
Should I use LRFD or ASD?
Either is permitted under most modern building codes (e.g., IBC references both). LRFD uses factored loads with resistance factors (φ); ASD uses service-level loads with safety factors (Ω). Use whichever your project's load combinations and jurisdiction require — don't mix factored LRFD loads with ASD capacities or vice versa.
Why did my section pass axial and bending but fail web crippling?
Web crippling is a separate local bearing check at concentrated loads and reactions — a thin, unstiffened web can crush locally even when the member's overall axial and bending capacity is more than adequate. Add a bearing stiffener, increase bearing length, or thicken the section locally.
What does the governing buckling mode (global, local, distortional) tell me?
It tells you which fix actually works. Global buckling governed by slenderness → shorten the unbraced length or add bracing. Local buckling → thicken the flange or web, or add intermediate stiffeners. Distortional buckling → increase the lip length or add an edge stiffener.
Can I use this for built-up (back-to-back or boxed) sections?
Not directly — the section property and buckling formulas here assume a single, open thin-walled shape. Built-up sections need combined properties and different web-crippling coefficients (multi-web equations), which this simplified tool doesn't include yet.
Why do screw connections use a much lower φ factor (0.50) than member checks (0.85–0.90)?
Fastener capacity has more installation-related variability (torque, edge distance, hole alignment) than a rolled or formed steel member, so AISI applies a more conservative resistance factor to connections.
Does switching units convert my existing input values?
No — the unit toggle only changes field labels, not values. Re-enter your inputs in the new unit system after switching, or complete your calculation before changing units.
Ready to run your own numbers?
Open the interactive Cold-Formed Steel Design Calculator to check section properties, axial/flexural/shear capacity, web crippling, and screw connections in real time.
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