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Stair Calculator

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Enter the total rise (floor-to-floor height) and your target step height to find the number of steps, the exact riser height, and the stringer length needed.

Stair Calculator

Live
Number of steps
14
Actual riser height
7.71 in
Total run
130 in
Stringer length
14.08 ft
Most residential codes cap riser height around 7.75 inches and require a minimum tread depth around 10 inches - check your local code.

The formula

Number of steps = round(Total rise / Target riser height) Actual riser height = Total rise / Number of steps Total run = (Number of steps − 1) x Tread depth Stringer length = sqrt(Total rise^2 + Total run^2)
Example

A 108-inch total rise (9 feet floor-to-floor) targeting 7.5-inch risers with a 10-inch tread: 14 steps, each an actual 7.71 inches - close to the target since risers must divide evenly into the total rise. The stringer needs to be about 14.08 feet long.

Step-by-step guide

  1. Measure the total rise - the exact vertical distance from the lower finished floor to the upper finished floor.
  2. Set a target riser height - 7-7.5 inches is common and comfortable for most people.
  3. Enter your tread depth - 10-11 inches is typical for residential stairs.
  4. Read the actual riser height - it will always be slightly different from your target, since the total rise must divide evenly across a whole number of steps.

Why "actual" riser height matters so much

Building codes and basic safety both depend on every riser in a staircase being the same height - even a small inconsistency (a quarter inch or more) is a well-documented tripping hazard, since people unconsciously expect each step to match the last. That's why this calculator always rounds to a whole number of steps and recalculates the exact riser height needed, rather than letting the last step be a different height than the rest.

Common mistakes

Building the last step to a different height to hit an exact target riser height - always use the calculated actual riser height for every single step, not the target.
Measuring total rise from subfloor to subfloor instead of finished floor to finished floor - flooring thickness on both levels changes the true rise.

Frequently asked questions

What riser height and tread depth does code typically require?

Requirements vary by jurisdiction, but many residential codes cap risers around 7.75 inches maximum and require at least 10 inches of tread depth. Always confirm your specific local code before building.

What's a stringer?

The stringer is the diagonal structural board that the treads and risers attach to - most staircases use two or three stringers running the full diagonal length of the stairs.

Why is my actual riser height different from what I typed?

Your target is just a starting point - the calculator finds the whole number of steps closest to that target, then recalculates the exact riser height so every step is perfectly equal.

Should I consult a professional for stair building?

Stairs are a common source of home injuries, and most jurisdictions require a permit and inspection for new or rebuilt stairs. This calculator helps with planning, but a licensed contractor should handle the actual build for anything beyond a simple deck step.

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