Stair calculator

Enter the floor-to-floor height. You get the number of steps, the exact riser height, the total run and how long your stringers need to be.

Steps (risers): –
Riser heighthow tall each step is: –
Framing squaretongue / blade, to mark the stringer: –
Treads: –
Total runfloor space the stair takes: –
Stringer lengththe notched boards that carry the steps: –
Angle: –
Code check (IRC): –
Comfort (2R + T)24" to 25" feels natural: –

What to buy

How the stair math works

Every step must be the same height, so the calculator splits the total rise into equal risers that stay under your maximum. The number of treads is one less than the number of risers, because you step onto the upper floor at the top.

Risers = total rise ÷ max riser, rounded up. Riser height = total rise ÷ risers.

Stringer length = √(rise² + (run + one tread)²)

Worked example

A basement stair with 108 inches floor to floor: 108 ÷ 7.75 = 13.9, so you need 14 risers of 7 11/16 inches each. With 13 treads at 10 inches the stair runs 130 inches, about 10 feet 10 inches across the floor.

Before you cut stringers

Measure total rise in two or three spots. Floors are rarely level.
Subtract the tread thickness from the first riser on the stringer so the bottom step matches the rest.
Buy stringer stock at least one size longer than the stringer length shown here.

Questions people ask

What is the maximum riser height for stairs?

The International Residential Code (IRC R311.7.5.1) allows a riser up to 7 3/4 inches and a tread at least 10 inches deep. Many local codes follow it, but check yours.

How many steps do I need?

Divide the total rise by 7 3/4 and round up. That gives the number of risers. There is always one fewer tread than risers, because the top floor is the last step.

How do I measure total rise?

Measure from the finished floor at the bottom to the finished floor at the top. Include flooring that is not installed yet, or the first and last steps will be uneven.

What is a comfortable stair?

A common rule is twice the riser plus the tread should land between 24 and 25 inches. A 7 1/2 inch riser with a 10 inch tread gives 25.