How do I calculate stair risers and treads?

Enter total rise (floor to floor) and preferred riser height. The calculator divides total rise by riser height to get the number of risers, then computes exact riser height, tread run, and total run. It checks each measurement against IRC residential code limits.

What is the formula for stair stringer length?

Stringer length equals the square root of total rise squared plus total run squared. The calculator solves this from your rise and run inputs, shows the measurement, and generates a printable stair diagram with all dimensions labeled.

What stair dimensions meet building code?

IRC code limits risers to 7 and three-quarter inches maximum per step and requires treads of at least 10 inches. The calculator flags any violations in a code-check summary so you know if your layout passes before cutting stringers.

Layout

Stair Rise / Run Calculator

Calculate risers, treads, total run, stringer length, and a code-check summary with a printable stair diagram.

Stairs feel simple until the layout hits real lumber, uneven floors, and code checks. This stair calculator helps you turn total rise into a buildable plan: riser count, exact riser height, tread depth, total run, and stringer length, so you can cut with fewer surprises.

How it works

Start by measuring total rise, the vertical distance from the lower finished floor to the upper finished floor. For a rough riser count, divide total rise by 7 inches, then round to a whole number. Exact riser height equals total rise divided by number of risers. Choose a tread depth, often checked against a typical 10 inch minimum, then calculate total run as number of treads multiplied by tread depth. In a standard stair, the number of treads is usually 1 fewer than the number of risers. Stringer length comes from the Pythagorean theorem: square total rise, square total run, add them, then take the square root. Keep risers near the typical 7.75 inch maximum and use the 7-11 rule as a practical comfort check.

Worked examples

Deck stairs with an 84 in. total rise 84 ÷ 7 = 12 risers. Exact riser height = 84 ÷ 12 = 7 in. Treads = 11. With a 10 in. tread depth, total run = 11 × 10 = 110 in. Stringer length = √(84² + 110²) = 138.4 in. This layout gives 12 risers at 7 in., 11 treads at 10 in., and a stringer length of about 138.4 in.
Garage stairs with a 96 in. total rise 96 ÷ 7 = 13.7, so use 14 risers. Exact riser height = 96 ÷ 14 = 6.86 in. Treads = 13. With a 10 in. tread depth, total run = 13 × 10 = 130 in. Stringer length = √(96² + 130²) = 161.6 in. This layout keeps the riser under the typical 7.75 in. maximum, with 14 risers, 13 treads, and a stringer length of about 161.6 in.
Porch stairs using an 11 in. tread 102 ÷ 7 = 14.57, so use 15 risers. Exact riser height = 102 ÷ 15 = 6.8 in. Treads = 14. With an 11 in. tread depth, total run = 14 × 11 = 154 in. Stringer length = √(102² + 154²) = 184.8 in. This layout pairs a 6.8 in. riser with an 11 in. tread, close to the common 7-11 comfort target.

FAQ

How do I calculate the number of stair risers?

Measure the total rise, then divide by 7 inches for a rough riser count. Round to a whole number, then divide the total rise by that riser count to get the exact riser height.

How many treads do I need?

For a typical straight stair, the number of treads is usually 1 fewer than the number of risers, because the upper floor acts as the final step surface.

How do I calculate stair stringer length?

Use the Pythagorean theorem. Square the total rise, square the total run, add those numbers together, then take the square root. The result is the diagonal stringer length before layout details and cuts.

What stair code limits should I check?

Common checks include a riser near a 7.75 inch maximum and a tread near a 10 inch minimum. Local code can vary, so always verify requirements for your project before cutting stringers.