Build stairs that feel right the first time. Enter your total rise and get the riser count, exact riser height, tread count, total run and stringer length — plus a check against the comfort rule.
Your stair opening
How the math works
Risers = Total rise ÷ Target riser height (rounded), then Actual riser = Total rise ÷ Risers. Treads = Risers − 1, and Stringer = √(Run² + Rise²).
The calculator rounds to the nearest whole riser count, then divides your actual rise evenly so every step is identical — the key to stairs that feel safe. The stringer length is the hypotenuse of the total run and total rise triangle.
Tips for building stairs
- The comfort rule: 2 × riser + tread should land between 24″ and 27″. Outside that range stairs feel steep or sluggish — the calculator checks this for you.
- Measure finished floor to finished floor. Include flooring thickness on both levels or your first and last risers will be off.
- Lay the stringer out full-size on a sheet of plywood or the floor before cutting, and check the first/last riser against reality.
- Building deck stairs? Count your deck boards first with the deck board calculator and posts with the wood fence calculator.
Frequently asked questions
What is the ideal riser height?
Most building codes allow a maximum riser of 7¾″, and the comfort sweet spot is 7″ to 7.5″. Lower risers feel easier but need more run; this calculator targets 7.5″ by default.
Why is there one less tread than risers?
The top “tread” is the upper floor or deck surface itself — you step onto it, not onto a board. So a 13-riser stair has 12 tread boards plus the landing.
How long should the stringer board be?
Buy a board longer than the calculated stringer length — the calculator gives the exact hypotenuse, but you need extra for the top and bottom cuts. A 2×12 is the standard stringer stock.
What if my total run is limited by space?
Shorten the tread depth (down to about 10″ minimum for comfort) or accept a steeper riser. If the layout falls outside the comfort rule, the calculator will warn you — very steep stairs may need a different design like alternating treads.