Free online construction calculators built from the IRC tables
Span, concrete, stairs, roofing and materials. Every result names the IRC 2021 (International Residential Code) or AWC table it came from. Free, no signup, printable, imperial, and it works on the phone on site.
Construction calculators by trade
Structural span calculators
Joist, rafter, beam and header spans read straight from the code tables.
All 14 span tools →Concrete calculators
Slabs, footings, post holes and gravel in cubic yards or in bags.
All 13 concrete tools →Stair calculators
Stringer layout, rise and run, and baluster spacing, drawn to scale.
All 3 stair tools →Roofing calculators
Pitch, roof area, rafter length and shingle bundles for hip or gable.
All 10 roofing tools →Materials calculators
Board feet, tile, drywall, siding, decking and fence parts with waste.
All 18 material tools →Where the numbers come from
A real result from the floor joist span calculator.
The table number prints with the answer
Every code-based result shows the table it was read from, like Source: IRC Table R502.3.1(2). You can check our answer against the code book instead of taking it on trust.
Real inputs, not one box
A span depends on species, grade, lumber size, spacing, load and how much sag you allow, which the code calls deflection and writes as L/360. You set each one, so the answer fits your build.
Printable, with the assumptions attached
Results print on one page with every input listed underneath, so the crew, the inspector, or you in six months can see exactly what was entered.
What these don't do: no cost estimating, no pricing, no engineering design. Geometry, quantities and code-table lookup — for homeowners, carpenters, deck builders and concrete crews.
Building code guides
How to read a span table
Species, grade, spacing and deflection in the order the IRC table actually lists them.
IRC stair code, in plain English
Rise, run, headroom and handrail limits, with the section number beside each one.
Deck framing and the AWC tables
Which deck spans come from DCA 6, and where your local amendments override it.