How to measure total rise
Total rise is the vertical distance from the finished floor at the bottom of the stairs to the finished floor at the top. Measure it where the stairs will actually go, because floors are not always level. If the finished flooring is not installed yet, add its thickness at the top and subtract it at the bottom so every step comes out the same height.
How the calculation works
Number of risers = total rise ÷ maximum riser height, rounded up
Riser height = total rise ÷ number of risers
Number of treads = risers − 1 (the top floor acts as the last step)
Total run = treads × tread depth
Stringer length = √(total rise² + total run²)
In the example above, a total rise of 108 inches (9 feet) divided by a 7 3/4 inch maximum needs 14 risers, each 7 11/16 inches tall. There are 13 treads; at 10 inches deep they cover a total run of 130 inches, or 10 ft 10 in. The stringers must be at least 169 inches long, about 14 feet, so you would buy 16 ft boards.
Common code limits for stairs in homes
Most US states and cities base their residential rules on the International Residential Code (IRC). Its main limits for stairs are:
| Rule | IRC limit |
|---|---|
| Maximum riser height | 7 3/4 in |
| Minimum tread depth | 10 in |
| Difference between the tallest and shortest riser, or deepest and shallowest tread | 3/8 in or less |
| Minimum headroom | 6 ft 8 in |
| Minimum stair width | 36 in |
Local codes can add their own amendments, and commercial buildings follow stricter rules (typically 7 inch risers and 11 inch treads). Check with your local building department before you build.
Making stairs comfortable
A traditional carpenter's rule says two risers plus one tread should add up to roughly 24 to 25 inches. Stairs in that range match a normal walking stride, so they feel natural to climb. Very short risers with deep treads, or tall risers with shallow treads, feel awkward even when they meet the code. The calculator shows this check for your numbers.
Frequently asked questions
How many steps do I need for 8 feet?
For a total rise of 96 inches with a 7 3/4 inch maximum riser, you need 13 risers of about 7 3/8 inches each and 12 treads.
What is the difference between a riser and a tread?
The riser is the vertical part of each step and the tread is the horizontal part you step on. A staircase always has one more riser than treads, because the top floor serves as the last tread.
Does tread depth include the nosing?
No. Tread depth is measured from the face of one riser to the face of the next. Under the IRC, stairs with solid risers and treads less than 11 inches deep also need a nosing that sticks out 3/4 to 1 1/4 inches past the riser.
How long should stair stringers be?
At least the diagonal length of the staircase, which the calculator works out from the total rise and total run. Buy boards a foot or two longer to allow for the cuts at the top and bottom.
This calculator helps you plan a staircase. Stairs are a safety-critical part of a house: confirm the design with your local building department or a professional before building.