Stair calculator: convert total rise into riser height, tread depth, stringer length, and step count that meet building code. Free, no signup, runs locally.
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Every figure above is calculated locally in your browser from the assumptions shown. No inputs are sent anywhere. See the methodology section below for the formulas used.
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This stair calculator turns your total rise and target riser height into a complete set of stair dimensions. It first finds the number of risers, then calculates the actual riser height, the number of treads, and the stringer length needed. Use the result to build your stringer and lay out steps accurately, without any signup or data upload.
15 risers from a 108 inch rise at 7.5 inch target.
Formula & evidence
How this calculator works
Reviewed July 2026 · BoringToolsKit Editorial Team
Sources support the method, terminology, or planning context. Editable assumptions remain your responsibility.
Assumptions to verify
The stair is a straight flight with equal risers.
The target is used to choose a count; local code controls maximum riser and minimum tread.
Structural sizing, nosing, landings, headroom, guards, and handrails are excluded.
Frequently asked questions
Do I need to create an account or sign up to use the stair calculator?
No. The stair calculator is entirely no-signup and runs directly in your browser — nothing is saved or uploaded.
Is my data safe when using the stair calculator?
Yes. All calculations happen locally on your device in the browser. No personal data or input values are stored, transmitted, or collected.
What measurements does the stair calculator use to generate stair dimensions?
The stair calculator uses your total rise (floor-to-floor height), desired tread depth, and riser height to compute step count, run length, and stringer angles for safe, code-compliant stairs.
BoringToolsKit. “Stair Calculator.” boringtoolskit.com/stair-calculator/ (reviewed July 2026). Free to reference in articles, syllabi, and answer posts with a link.
Privacy: Inputs and results stay in this browser. Results are planning estimates based on your inputs; verify assumptions and current rules before making decisions.
Worked example: a 108 inch deck rise
Say the total rise from grade to deck surface is 108 inches and you target a 7.5 inch riser. The calculator divides 108 by 7.5 to get exactly 14.4, then rounds up with the ceiling function, giving 15 risers. That round-up is the key step: you cannot build 14.4 risers, and spreading the remainder across 15 steps is how the geometry absorbs it.
The actual riser height becomes 108 / 15 = 7.2 inches, comfortably inside the common residential 7.75 inch limit. With 15 risers you get 14 treads, since the top tread is the deck surface itself. At a chosen tread depth of 11.5 inches, total run is 14 x 11.5 = 161 inches, or 13 feet 5 inches. The stringer slope length is sqrt(108^2 + 161^2) = sqrt(11,664 + 25,921) = sqrt(37,585), which is about 193.87 inches, so standard 16 foot lumber covers each stringer with roughly a foot to spare before notching.
Notice the trade the round-up made: total run depends on riser count, so an extra riser adds a full tread of run. If 161 inches overruns a small yard, re-running the same 108 inch rise at 15.6 inches of rise per... rather, at a tighter 7.2 inch target, yields ceil(108/7.2) = 15 as well, showing the layout is already near its minimum run for code-compliant risers.
Where the geometry stops: framing reality
The output assumes the stringer is cut from a straight, uniformly strong board, and numbers start failing before lumber does. A 2x12 stringer notched for 7.2 x 11.5 treads loses roughly 1.5 inches of depth at each notch; IRC guidance caps notch depth at half the member, and on a 194 inch span many builders double or triple stringers, or bolt a steel channel, because a single notched 2x12 can feel springy under load well before any code test fails.
Counting rules also shift the arithmetic at the edges. Some jurisdictions count the top riser differently when the upper landing is poured concrete versus a deck rim, and a mid-run landing inserts itself as a tread-plus-riser pair that this calculator does not model: a 3 foot by 3 foot landing adds about 36 inches of run and resets nothing else in the numbers above. Headroom is the silent constraint the tool cannot see: with a 194 inch slope length at roughly 34 degrees, a covered stairwell needs about 80 inches of clear height measured plumb from the nosing line, which often forces a gentler angle, more risers, and more run than the geometry alone suggests.
Field tolerance matters too: a 1/8 inch difference in riser height across consecutive steps, the common maximum, is easy to exceed when the first riser lands on sloped grade. Measure from finished surface to finished surface, not framing, since finish flooring can add 3/4 inch or more to total rise.
