Steel Joist Spacing Chart & Span Tables
Steel joist spacing and span are critical factors that determine the strength, stability of structural systems in buildings. This complete steel joist spacing chart and span guide explains how to correctly assess joist dimensions, spacing, and load limits using data from the Steel Joist Institute (SJI) and manufacturer design manuals.
Whether you’re working with K-Series, LH-Series, or open web steel joists, understanding how joist size, spacing, and span interact ensures safe, efficient, and cost-effective structural design.
In this guide, I’ll walk you through how to determine correct steel joist spacing, what tables and charts to use, and how different factors like load and joist type affect your design. Whether you’re building a deck, a mezzanine floor, or a full commercial structure—this is for you.
Key Takeaways:
- Common steel joist spacing: 16" to 24" on center for most builds.
- Heavier loads need closer spacing (12" O.C.).
- Open web joists may span up to 11 feet apart in some roof systems.
- Always check Steel Joist Institute (SJI) span tables and local codes.
- Use a Steel Joist Calculator or Steel Beam Calculator to confirm spacing and load.
- A 25–75mm gap from the wall to the first joist helps reduce vibration.
What Is Steel Joist Spacing?
Steel joist spacing refers to the distance between individual joists that support a floor, roof, or deck structure. Proper spacing helps distribute loads evenly and prevents deflection or failure.
Common Maximum Spacing:
- 600 mm (24 in) — typical for cold-formed steel joists with wood panel sheathing.
- 1.83 m (6 ft) — common for steel joists supported by masonry walls.
Open Web Joists:
- Roof spacing can reach up to 11 ft, depending on live and dead loads.
- Floor joists are usually spaced 1.67 ft – 3.67 ft apart for better rigidity.
Steel Joist Spacing Chart & Span Guide (With Tables)
Steel joist spacing depends on load, span, and design requirements, but standard spacing typically ranges from 600 mm (24 inches) to 1.83 m (6 feet).
This steel joist spacing chart and guide explains how to determine the correct spacing for steel, metal, and open web joists using span tables, K-Series specifications, and Steel Joist Institute (SJI) standards.
Whether you’re designing a floor, roof, or rafter system, understanding proper joist spacing ensures strength, safety, and efficiency in every construction project.
When I first tried figuring out joist spacing for my metal workshop floor, I thought, “How hard can it be?” Well, about 30 measurements, two coffee breaks, and a few wrong calculations later, I realized spacing steel joists isn’t guesswork. It’s a careful balance between load, span, and code requirements.
Steel Joist Spacing Chart (General Reference)
| Joist Type | Typical Spacing | Application | Notes |
|---|---|---|---|
| Cold-formed steel joists | 12 in O.C. (300 mm) | Heavy loads, long spans | Increases floor rigidity |
| Standard steel joists | 16 in O.C. (400 mm) | Residential floors | Most common spacing |
| Structural joists | 19.2 in O.C. (490 mm) | Light commercial | Balances material use |
| Metal framing joists | 24 in O.C. (600 mm) | Roof or ceiling systems | For larger, stronger joists |
| Masonry-supported joists | 6 ft (1.83 m) | Industrial buildings | Per the SJI manual |
| Open web joists | Up to 11 ft | Roof systems | Span depends on load & code |
Standard Steel Joist Spacing (in Inches and Millimeters)
| Application | Common Spacing (O.C.) | Metric Equivalent (mm) | Notes |
|---|---|---|---|
| Light floors | 12" | 300 mm | Heavier loads, tighter spacing |
| Residential | 16" | 400 mm | Most common for home floors |
| Light commercial | 19.2" | 480 mm | Material-saving alternative |
| General floors | 24" | 600 mm | For lighter loads |
| Masonry support | 72" (6 ft) | 1830 mm | With strong wall supports |
| Roof systems | Up to 132" (11 ft) | 3350 mm | Open web steel joists |
How to Determine the Correct Steel Joist Size and Spacing
To determine joist spacing, you need to consider five main factors: load, span, flooring type, design code, and manufacturer specifications.
Here’s a simple process:
- Identify total load – include live (people, furniture) and dead (materials) loads.
- Measure span length – longer spans require closer spacing or deeper joists.
- Check the flooring system – heavy concrete topping? Reduce spacing.
- Consult span tables – always verify against the SJI load tables.
- Confirm with a calculator – use a Steel Joist Calculator for precision.
If you’re ever unsure, 16 inches O.C. is a good starting point for most floors.
When I helped a friend build his small steel deck, we learned that changing from wood to steel meant more than swapping materials. The load-carrying behavior changes completely. We had to re-check every spacing using the Steel Joist Institute (SJI) manual.
Consult Manufacturer Load Tables: Use charts provided by manufacturers or the Steel Joist Institute (SJI) to find the right joist type, depth, and gauge for your load and span.
- Example: A 24CJ 1400/800/240 joist has a 24-inch depth, 1,400 plf total load, 800 plf live load, and 240 plf dead load.
Use Design Specifications: Follow Allowable Stress Design (ASD) or Load and Resistance Factor Design (LRFD) methods to ensure the joist meets structural requirements.
Account for Collateral Loads: Include weights from ducts, pipes, and sprinkler systems—either as uniform or concentrated loads.
Distribute Loads Across Joists: In multi-joist systems, load sharing increases efficiency, but each joist must still meet its individual capacity.
Typical Steel Joist Spacing and Span Table
| Joist Type | Depth (in.) | Typical Span (ft) | Common Spacing (in.) | Common Use |
|---|---|---|---|---|
| K-Series | 8–30 | 10–60 | 24–48 | Floors, roofs (light to moderate loads) |
| LH-Series | 18–48 | 60–96 | 48–60 | Long-span roofs, warehouses |
| DLH-Series | 52–120 | 96–144 | 60–72 | Extra-long-span roofs |
| CJ-Series (Composite) | 10–36 | 15–75 | 24–48 | Composite floor systems |
Example: Determining the Maximum Span
To determine the maximum span for a K-Series steel joist:
- Identify the joist depth (e.g., 18K6).
- Use the SJI load table to find allowable spans for given live and dead loads.
- Adjust spacing and load values as needed for your building type and design load.
Steel Joist Span Tables and Load Capacity
Joist span is how far a joist can stretch between supports without bending excessively. Steel joists can span much farther than wood, but the span still depends on joist size, series, and spacing.
Below is a simplified span table for reference (values rounded for illustration):
| Joist Type | Depth (in.) | Max Span (ft) | Typical Spacing (O.C.) |
|---|---|---|---|
| K-Series 8K1 | 8 | 20 | 24" |
| K-Series 12K3 | 12 | 30 | 24"–48" |
| LH-Series 16LH2 | 16 | 45 | 48"–72" |
| DLH-Series 24DLH | 24 | 60+ | 72"–132" |
Pain point: Builders often pick joists based on span alone.
Solution: Always match span and spacing to the intended load using verified data from the Steel Joist Institute (SJI).
Even a small adjustment in spacing can change your total material cost and load performance dramatically.
Open Web Steel Joist Spacing
Open web joists are commonly used in commercial roofs and long-span floors. Their spacing can range from 1.67 feet to 11 feet, depending on the load and joist depth.
I remember seeing an industrial building where open web joists were spaced 10 feet apart—my first thought was, “Is that even safe?” It was because those joists were DLH series, designed for long spans with wide spacing.
Typical open web spacing examples:
| Application | Spacing Range (ft) | Notes |
|---|---|---|
| Floor systems | 1.67–3.67 | Closer spacing for vibration control |
| Roof systems | 6–11 | Lighter loads allow wider spacing |
| Warehouse roofs | 8–10 | Common for steel trusses |
Pro tip: Wider spacing reduces joist count but can increase vibration. If you prefer a “stiffer” floor feel, go slightly closer, even if the code allows more distance.
Common Mistakes in Joist Spacing
Even pros mess this up sometimes. I’ve seen floors creak like old ships just because of spacing errors.
Here are a few common mistakes and how to avoid them:
- Ignoring manufacturer tables – always check the official SJI manual or product sheet.
- Over-spanning small joists – deeper joists or closer spacing fix deflection.
- Mixing joist types – don’t use open web and solid web joists in the same run without proper engineering.
- Skipping bridging – lack of bridging can cause joist twist and vibration.
- Wrong bearing length – most joists need at least 2.5 inches of bearing.
If your floor feels bouncy, chances are spacing or bridging is to blame. Recheck your layout using a joist span calculator.
Steel Joist Institute (SJI) Standards
The Steel Joist Institute (SJI) sets the standards for design, load capacity, and installation of steel joists in the U.S. and beyond.
Their manuals contain:
- Span tables for K-Series, LH-Series, and DLH-Series.
- Design charts showing load capacity vs. span.
- Guidelines for spacing and bearing requirements.
Every engineer I know swears by the SJI manual. If you’re building in Australia or Canada, similar standards exist through AS/NZS 4600 and CSA S136.
Determining Joist Size and Spacing
If you’re wondering, “What size joist do I need for a 12-foot span?”—you’re not alone.
A few rough rules of thumb (always verify with tables):
- 12 ft span → 8" to 10" deep joist, spaced 16" O.C.
- 20 ft span → 12" to 16" deep joist, spaced 24" O.C.
- 30 ft span → K12 or LH-Series joist, spacing 36"–48" O.C.
Formula to start with:
Spacing = (Span × Load Factor) ÷ Joist Strength
That’s where the Steel Joist Calculator helps—it eliminates the guesswork.
Joist Spacing Diagram
Below is a simple layout concept:
|<-- 16" O.C. -->|<-- 16" O.C. -->|<-- 16" O.C. -->|
┌───────┬───────┬───────┬───────┬───────┬───────┐
│ J1 │ J2 │ J3 │ J4 │ J5 │ J6 │
└───────┴───────┴───────┴───────┴───────┴───────┘
Maintain a 25–75 mm gap from the wall to the first joist for expansion and vibration control.
Regional Standards and Practices (Australia, UK, US)
| Region | Common Spacing | Standards/Code | Notes |
|---|---|---|---|
| United States | 12", 16", 24" O.C. | SJI, IBC | Most widely referenced tables |
| Australia | 450mm, 600mm O.C. | AS/NZS 4600 | Cold-formed steel framing |
| United Kingdom | 400mm, 600mm O.C. | BS 5950 | Similar to metric practice |
Even though these numbers vary slightly, the logic stays the same—closer spacing equals stronger support.
How to Calculate Joist Spacing Manually
If you don’t have a calculator handy, here’s a basic method:
- Multiply total load (psf) by span (ft).
- Divide that by the capacity of one joist.
- Adjust spacing until load per joist ≤ rated capacity.
Example: If your load is 50 psf and your joist supports 600 lbs, spacing roughly equals (600 ÷ 50) = 12 ft, or 144 inches O.C. That’s way too wide, so reduce spacing until you’re within limits.
Tip: That’s exactly why span tables exist—they save you this headache.
Steel Joist vs. Steel Beam Spacing
People often mix these up. A beam supports joists; joists support the floor or roof.
| Component | Typical Spacing | Purpose |
|---|---|---|
| Steel Beam | 6–12 ft | Supports joists or decking |
| Steel Joist | 12–24 in | Supports sheathing or flooring |
| Metal Stud | 16–24 in | Supports walls, non-load-bearing |
If you’re designing a structural layout, remember: beams carry joists, not the other way around.
Using a Steel Joist Calculator
A Steel Joist Calculator takes your span, load, joist depth, and material properties to estimate spacing.
Enter:
- Joist depth (in inches)
- Span (in feet)
- Load (psf)
- Desired deflection limit
Output:
- Recommended spacing (O.C.)
- Required joist weight (lb/ft)
- Suitable joist type (K, LH, or DLH)
Many builders also use a Steel Beam Calculator for complementary design checks.
How to Avoid Repetitive Joist Patterns
Repetition can make installation easy, but sometimes it's a problem—especially with vibration and sound. Staggering joist placement slightly or using alternating bridging can reduce “drum” noise.
If you’ve ever noticed that “boing” sound on metal floors, that’s a rhythmic resonance. It’s minor but annoying. A small adjustment in spacing or bridging pattern fixes it instantly.
Quick Reference Chart: Maximum Joist Spacing
| Joist Type | Max Spacing (ft) | Load Condition | Use Case |
|---|---|---|---|
| Cold-formed steel | 2 ft | Light floor | Residential |
| K-Series | 6 ft | Standard load | Commercial floors |
| LH-Series | 8 ft | Heavy load | Roof systems |
| DLH-Series | 11 ft | Light roof | Long-span roofs |
Final Thoughts
Figuring out steel joist spacing can seem tedious, but once you understand the balance between load, span, and stiffness, it becomes second nature.
When I finally got my workshop floor right—using 16" O.C. spacing and 10" K-Series joists—the difference was night and day. The floor felt solid, quiet, and reliable.
Whether you’re an engineer, contractor, or DIY builder, remember:
- Never guess joist spacing.
- Always verify with the Steel Joist Institute tables.
- And if you’re still unsure—use the Steel Joist Calculator to confirm.
Your project will thank you later.
