Your truss, drawn to scale
Fink web
Need a roofing contractor for this project?
Take the span, pitch and truss count you just worked out to a roofing pro. They handle the installation, the replacement or the repair, and can price the finished roof rather than just the frame.
- Roof installation
- Roof replacement
- Roof repair
Planning estimates only. Always confirm against a sealed engineered truss design before ordering or building.
- Calculators
- 17 Calculators
- Truss shapes
- 11 Truss shapes
- Data stored
- 0 Data stored
- Forever
- Free Forever
The basics
What is a Steel Truss?
Steel is chosen for span, for fire classification, or for environments that destroy timber. It is rarely chosen on price.
Where it wins is clear: non-combustible construction, termite and rot (opens in a new tab) immunity, dimensional stability, and spans timber simply cannot reach. Every member also performs exactly as designed, with no knots or grain variation to allow for.
Where it loses is cost and heat. Steel conducts heat far better than wood, so every member crossing an insulated assembly is a thermal bridge (opens in a new tab). Without continuous exterior insulation or a proper thermal break you get cold lines on the ceiling and condensation on the steel inside the assembly.
- Long clear spans Structural steel routinely covers 40 to 150 ft, which is well past what timber can reach.
- Non-combustible classification Required in many commercial and multi-family applications regardless of every other consideration.
- Thermal bridging Needs continuous exterior insulation or a designed thermal break, and that detailing is often the first thing cut.
- Fire resistance still needs designing Steel does not burn but loses strength when hot. Rated assemblies need coating, spray protection or an encasing membrane.
Replacing a spreadsheet
This calculator does what a steel truss design spreadsheet does for the planning stage: member lengths, weight take-off, load per truss. Print the results page for your file, then have the sections sized by an engineer.
The maths
Steel Truss Formula
Steel truss weight take-off
The 10% allowance covers connection material. Tonnage is what you price, ship and size the crane from.
Method
How to Calculate a Steel Truss
Steel truss calculation follows the same geometry as timber, but the number that drives everything downstream is weight rather than board feet.
- 1 Set span and pitch Steel trusses commonly run flatter than timber. 2:12 to 4:12 is typical on industrial roofs.
- 2 Choose the section class Light-gauge for spans up to about 40 ft, structural steel beyond that or where fire rating drives the choice.
- 3 Set the spacing Steel trusses usually sit 4 ft to 20 ft apart with purlins between them, not at 24 in on centre.
- 4 Read the weight Total tonnage is what you price, what you ship and what determines the crane. It is the primary output here.
Steel's strength-to-weight ratio (opens in a new tab) in tension is far higher than construction lumber, and unlike timber it has no knots, no grain direction and no moisture content to allow for. A steel member performs as the numbers say it will.
That predictability is what buys the span. A long-span timber truss has to be designed conservatively because the lumber is variable; a steel truss can be designed close to its actual capacity. Combined with the freedom to fabricate any depth, that is how steel roofs reach 100 ft and beyond.
Worked example
A 48 ft light-gauge steel truss at 4:12 with roughly 172 ft of member length, using a section at about 3.6 lb per foot, comes to around 620 lb before connections and about 680 lb with them. That is a crane lift, not a hand set. Section sizing itself is an engineer's call.
Where each material makes sense for a roof truss.
| Factor | Timber truss | Light-gauge steel | Structural steel |
|---|---|---|---|
| Practical span | Up to 60 ft | Up to 40 ft | 40 to 150 ft and beyond |
| Weight | Lightest per truss | Comparable to timber | Heaviest, crane required |
| Cost per truss | Lowest | 20 to 40% higher | Several times timber |
| Fire behaviour | Combustible, chars | Non-combustible, weakens when hot | Non-combustible, needs protection |
| Dimensional stability | Moves with moisture | Stable | Stable |
| Site modification | Never permitted | Never permitted | Never permitted |
Note: Steel conducts heat readily, so light-gauge steel trusses need a thermal break to avoid condensation at the members.
The tool
Why Choose Our Steel Truss Calculator
Steel jobs are priced, shipped and lifted by weight, so this calculator leads with tonnage rather than board feet.
- Weight is the headline Per truss and total, with a connection allowance already added.
- Light gauge or structural Switch section class and see the weight and cost move with it.
- Member lengths for fabrication Every chord and web measured from the drawn geometry, ready to hand to a fabricator.
- A spreadsheet replacement The planning-stage numbers a steel truss workbook gives you, without the version control problems.
More tools
Explore Related Truss Calculators
Calculators that pair with the steel tool, each running the same geometry engine.
- Wood Roof Truss Calculator Species, grade and size selection with a full board-foot take-off. Open calculator
- Roof Truss Span Calculator Check any span against chord size, species, pitch and load in one pass. Open calculator
- Roof Truss Weight Calculator Per-truss and total roof weight from a real member take-off. Open calculator
Get a free roofing quote
Roof installation, replacement and repair, quoted by a contractor who can visit the site. Bring your numbers from above and skip the guesswork on the rest of the job.
- Free quote
- No obligation
- Fast callback
Answers
Frequently Asked Questions
Common questions about steel roof truss calculator.
How far can a steel roof truss span?
Light-gauge cold-formed steel trusses commonly span up to 40 ft. Structural steel trusses span 40 to 150 ft routinely, and purpose-designed long-span trusses go well beyond that in arenas and hangars.
How do you calculate steel truss weight?
Total the lineal length of every member, multiply by the weight per foot of the section used, then add roughly 10% for gussets, bolts and welds. The calculator does this from the geometry it draws.
Are steel trusses cheaper than wood?
Not at residential spans. Expect 20 to 40% more for light-gauge steel than an equivalent timber truss. Steel becomes competitive past roughly 60 ft of span, and wins outright where non-combustible construction is required.
What size steel is used for roof trusses?
Light-gauge trusses typically use C-sections in the 1.5 to 3.5 in range at 12 to 20 gauge. Structural steel trusses use angles, channels or hollow sections sized by the engineer for the actual member forces.
Do steel trusses rust?
Galvanised light-gauge steel lasts decades in a dry, ventilated roof space. The realistic risk is condensation from thermal bridging rather than weather, which is why insulation and vapour detailing matter more than the coating specification.
Can steel and wood trusses be mixed in one roof?
Yes, and it is common. A steel girder truss carrying timber trusses over a wide opening is a standard arrangement. The connection detail and the differing deflection behaviour of the two materials both need designing.
References
Steel Truss Standards & References
Related calculators on this site, plus the standards and reference works the figures on this page are based on. External links open in a new tab.
Authoritative external references
- WIKI Steel frame, Wikipedia (opens in a new tab)
- WIKI Truss, Wikipedia (opens in a new tab)
- CODE International Code Council, model building codes (opens in a new tab)
- ORG SBCA, truss handling and bracing guidance (opens in a new tab)
- STD ANSI/TPI 1, Truss Plate Institute (opens in a new tab)
Codes and standards are revised on their own cycles. Confirm the current edition adopted in your jurisdiction with your local building department before relying on any figure.