By Zencalcy Editorial TeamLast reviewed About us
Every stair divides its total rise into equal risers. Building codes cap the riser at 7.75 inches and want the tread deep enough to land on, so the first step is finding how many risers fit, then sizing the stringer that carries them.
Risers, treads and stringer length for a flight of stairs.
risers = ⌈rise ÷ max riser height⌉ riser height = rise ÷ risers total run = (risers − 1) × tread depth stringer = √(rise² + run²)
The calculator targets a 7.5 inch riser so the finished stair lands under the common 7.75 inch code limit. Treads are one fewer than risers because the top riser lands on the upper floor, not on a tread.
| Symbol | Meaning |
|---|---|
| rise | Total rise, floor to floor. |
| tread | Horizontal depth of each tread. |
| run | Total horizontal run of the flight. |
108 ÷ 7.5 = 14.4, so 15 risers at 7.2 inches each; the run is 14 treads × 11 = 154 inches.
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Most US residential codes cap risers at 7.75 inches and require treads of at least 10 inches. Always confirm your local amendment.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026