Stair Calculator
Risers, treads, run, stringer length and angle with code checks.
What is the stair calculator?
The stair calculator helps you lay out a straight staircase. Starting from the total rise, the height from one finished floor to the next, it works out how many risers you need, the exact height of each riser, the number of treads, the total horizontal run, the length of the stringer and the angle of the stair. It then compares the result with common building code ranges and draws a simple side view so you can see the shape.
How to use it
- Choose metric (millimetres) or imperial (inches).
- Enter the total rise, measured from finished floor to finished floor.
- Enter the riser height you would like. Around 175 mm or 7 to 7 1/4 inches is comfortable.
- Either enter the tread depth you want, or switch to total run if your space is limited.
- Read the results and the pass or warn checks, then copy the summary for your builder or for cutting stringers.
What it calculates
- Risers: total rise divided by your desired riser, rounded to a whole number, so every step is equal.
- Treads: one fewer than the risers, because the upper floor forms the last step.
- Total run and stringer: treads x tread depth, and the pitch-line length from the square root of rise squared plus run squared.
- Angle: from the riser height and tread depth.
- Checks: riser 150 to 190 mm (7 to 7 3/4 in), tread at least 250 mm (10 in), and the comfort rule 2 x riser + tread between 600 and 650 mm (24 to 25 in).
Why equal steps matter
People get used to the rhythm of a stair within the first few steps. If one step is even slightly taller or shorter than the others, it is easy to trip. That is why the calculator divides the total rise into equal risers rather than using your desired height exactly. The 2R + T rule describes a comfortable stride: steep stairs with tall risers need shallower treads, and gentle stairs need deeper ones.
Tips before you build
Measure the total rise with the final floor finishes in mind, since adding tiles or carpet changes the height of the first and last steps. Remember headroom: most codes require about 2 m or 6 ft 8 in of clear height above the pitch line. Codes differ by country and between homes and public buildings, so treat the checks here as guidance and confirm with your local building authority. The stringer length shown is the pitch line, so allow extra timber for the cuts at the top and bottom.
Frequently asked questions
How many steps do I need for a 9 foot rise?
A 108 inch rise with a 7.25 inch target gives 15 risers of 7.2 inches and 14 treads. Enter your exact rise for a precise answer.
What is a comfortable stair angle?
Roughly 30 to 37 degrees is comfortable for most home stairs. Steeper stairs feel like a ladder and shallow stairs take up a lot of floor space.
Does the calculator guarantee my stair meets code?
No. It checks against common ranges, but building codes vary by country, region and building type. The results are estimates to help planning, so confirm with your local authority.