How the calculation works
Solid volume = width × tread × riser × n(n + 1) ÷ 2, with all dimensions in feet.
A worked example
Three solid steps at 3 ft wide, 12 in tread and 7 in riser total 10.5 ft³ before allowance.
What to check before using the result
- Solid equal steps only: not a suspended stair slab, hollow form, landing or engineered staircase.
- Tread/riser values are supplied geometry, not a code-compliance recommendation.
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References & product information
Method prepared 2026-10-21. See our calculation and editorial methods. Spotted a problem? Tell us about it.