Stair Calculator
Calculate the number of steps, riser height, tread depth, total run, stair angle and stringer length from the total rise, with a building code check
Last updated: November 5, 2026
How to Use the Stair Calculator
How to use the stair calculator
- Measure the total rise. Measure straight up from the finished lower floor to the finished upper floor. Include the thickness of any flooring you have not yet installed.
- Choose the unit system. Use inches, or switch to millimeters.
- Enter a preferred riser height. About 7 inches (178 mm) is comfortable. The calculator rounds to a whole number of equal risers.
- Enter the tread depth. Ten inches (254 mm) is the common minimum.
- Read the results. You will see the number of steps, the exact riser height, the number of treads, the total run you need, the stringer length, the angle and a check against typical code limits.
If the run is too long for the space, increase the riser height slightly (up to the limit) or add a landing. Mark the exact riser height on your stringer layout and make every step identical.
Formula & Methodology
Stair formulas
Every staircase is built from equal steps. The calculator uses these relationships:
Number of risers = Total rise ÷ Preferred riser height, rounded to a whole number
Actual riser height = Total rise ÷ Number of risers
Number of treads = Number of risers − 1, because the upper floor is the last step
Total run = Number of treads × Tread depth
Stringer length = √(Total rise² + Total run²)
Stair angle = arctan(Riser height ÷ Tread depth)
Worked example
The floors are 108 in (9 ft) apart. You want a riser of about 7 in and a tread of 10 in.
- Risers = 108 ÷ 7 = 15.4, so use 15 risers.
- Actual riser = 108 ÷ 15 = 7.2 in.
- Treads = 15 − 1 = 14.
- Total run = 14 × 10 = 140 in (11 ft 8 in).
- Stringer length = √(108² + 140²) = 176.8 in (about 14 ft 9 in).
- Angle = arctan(7.2 ÷ 10) = 35.8°.
- Comfort check: 2 × 7.2 + 10 = 24.4 in, within the usual 24 to 26 in.
Building code limits
In the United States the International Residential Code (IRC) is the model most states build on. It commonly allows a maximum riser of 7¾ in and a minimum tread of 10 in, and every riser in a flight should match closely. Headroom is typically at least 6 ft 8 in and stairs at least 36 in wide. Codes in the UK, Canada, Australia and elsewhere use different numbers, and local rules can be stricter, so always check with your building department before you cut stringers.
The comfort rule
A well-proportioned staircase usually satisfies 2 × riser + tread = about 24 to 26 inches. Steps that are tall with shallow treads feel steep, and low risers with very deep treads feel awkward to climb.
Riser versus rise, tread versus run
- Rise is the total height between floors. A riser is the height of one step.
- Run is the total horizontal length of the stairs. A tread is the depth of one step.
About Stair Calculator
Our stair calculator is a free, easy-to-use tool designed to help youcalculate the number of steps, riser height, tread depth, total run, stair angle and stringer length from the total rise, with a building code check. For professionals or those who need quick calculations, our calculator provides accurate results instantly.
Frequently Asked Questions
How do you calculate the number of steps in a staircase?
Divide the total rise (floor to floor) by the riser height you want, then round to a whole number. For a 108 in rise and a 7 in riser, 108 ÷ 7 = 15.4, so you need 15 risers. Divide the total rise by that number to get the exact riser height, 7.2 in.
What is the standard riser height and tread depth?
Residential stairs usually have a riser of about 7 to 7¾ inches and a tread of 10 to 11 inches. The IRC limits the riser to 7¾ inches and requires a tread of at least 10 inches. Always check your local code.
How do you find the stair stringer length?
Treat the stairs as a right triangle: the total rise is one side and the total run is the other. The stringer length is the hypotenuse, √(rise² + run²). For a 108 in rise and 140 in run, that is about 176.8 in. Buy a board longer than this so you can cut it.
Why are there fewer treads than risers?
The top step is the upper floor itself, so it is a riser with no tread of its own. A flight with 15 risers therefore has 14 treads, and the run is the number of treads times the tread depth.
What is a comfortable stair angle?
Most comfortable stairs sit between about 30 and 37 degrees. A 7 in riser with a 10 in tread is roughly 35 degrees. Steeper stairs feel harder to climb and are often not allowed by code.
What is the 2R + T rule for stairs?
Twice the riser height plus the tread depth should add up to about 24 to 26 inches. For a 7.2 in riser and a 10 in tread, 2 × 7.2 + 10 = 24.4 in, which feels natural to walk on.
How much headroom do stairs need?
Most residential codes call for at least 6 feet 8 inches of clear headroom measured straight up from the sloped line along the front edges of the treads. Check your local code, because it varies by country and by local authority.
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