Stair Calculator
Enter the total rise from finished floor to finished floor and get a flight of equal risers: the number of steps, the exact riser height, the tread depth, the total run and the stringer length.
Adjust the target riser and tread to suit your space, and check the result against your local code before cutting anything.
How to use the stair calculator
Measure the total rise, floor to floor.
Set your target riser and tread depth.
Read steps, exact riser, run and stringer.
Why use the Build Tally stair calculator
Equal risers guaranteed
Divides the rise into whole equal steps.
Total run shown
Check the flight fits before you cut.
Stringer length
Hypotenuse calculated for you.
Metric or imperial
Enter the rise in any unit.
How a flight is set out
Start with the total rise, measured from finished floor to finished floor — not from the subfloor, and not from the ground if flooring is going down later. Divide by your target riser height and round to a whole number, because every riser in a flight must be equal. Divide the total rise by that number and you have the exact riser. The number of treads is one less than the number of risers on a standard flight, and the total run is treads × tread depth. That run has to physically fit the space, which is the constraint people discover late.
Riser, tread and the rules that govern them
Comfortable stairs follow a relationship between riser and tread — the common rule of thumb is that twice the riser plus the tread lands somewhere around 24–25 inches. Building codes set hard limits on maximum riser height, minimum tread depth, minimum headroom and the permitted variation between steps in a flight, and those limits differ between jurisdictions and between residential and commercial work. Take the actual numbers from your local code rather than from any rule of thumb, including this one.
Stringers, nosing and the top step
Stringer length is the hypotenuse of the total rise and total run, and you need extra material beyond the calculated length for the cuts at each end. Nosing — the tread overhang — adds to the effective tread depth without adding to the total run, and codes usually specify a range for it. Watch the first and last riser: the thickness of the finished floor at the top and bottom changes them, and a top riser that ends up an inch different from the rest is both a code failure and a genuine trip hazard.
Read the guide: Deck Materials List: Working Out Boards, Joists, Posts and Fasteners
Frequently asked questions
How do I calculate stair risers?
Divide the total rise by your target riser height, round to a whole number, then divide the total rise by that number for the exact equal riser. The calculator does this.
What is a comfortable riser height?
Around 7 to 7.75 inches for residential stairs, but your local code sets the maximum — check it before cutting.
How deep should a stair tread be?
Typically 10 to 11 inches for residential stairs, again subject to your local code minimum.
How many treads for a given number of risers?
One less than the number of risers on a standard flight, because the upper floor forms the last surface.
How long does a stringer need to be?
The hypotenuse of the total rise and total run, plus extra for the end cuts. The calculator gives the calculated length.
Do stairs need a permit?
Usually yes for new or replacement flights, and they are commonly inspected. Check with your local building department.
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