Stair Calculator

Turn a floor-to-floor rise into a full stair layout: the number of steps, the equal riser height, the tread run and the stringer length to cut.

Use this free stair calculator to turn a floor-to-floor rise into a full stair layout: the number of steps, the equal riser height, the tread run and the stringer length to cut. Enter the total rise, drag the target riser, and set your tread depth to watch every number update at once. It works as a staircase calculator and a rise run calculator, and flags any riser or tread that falls outside common building code. As a stair stringer calculator it also gives the diagonal length to mark on your stringer board.

Staircase

Steps (risers)

15

7.2 in each riser · 14 treads

Treads
14
Total run
147 in
Stringer length
182.41 in
Tread board (with nosing)
11.5 in

Code checks

Riser 4–7.75 in (7.2)Tread ≥ 10 in (10.5)2R + T = 24–25 in (24.9)

A planning estimate using IRC guidance (7.75 in max riser, 10 in min tread). Landings, headroom, handrail height and your local code still apply, so confirm with your building department before you cut stringers.

How it works

  1. 1

    Enter the total rise

    Measure finished floor to finished floor above and type it in. Switch between feet and metres any time.

  2. 2

    Set the riser and tread

    Drag the target riser height and set the tread depth, the run per step. The step count and riser adjust to divide the rise evenly.

  3. 3

    Read the layout

    See the number of steps, the exact riser, the total run and the stringer length to cut, with pass or fail badges for the code limits.

Instant & 100% private — nothing is uploaded

Every calculation runs locally in your browser. The income, balances and goals you enter stay on your own device and are never sent to a server — nothing is stored, logged or shared.

Frequently asked questions

How do I calculate the number of stairs?
Divide the total rise by your target riser height and round to the nearest whole number for the riser count. The rise divided by that count gives the exact, equal riser height, which is what this stair calculator works out for you.
What is a comfortable riser and tread?
About 7 inches of rise with a 10 to 11 inch tread is the usual comfortable stair. The old rule is that twice the riser plus the tread should land between 24 and 25 inches; the calculator shows that figure and flags it if you drift outside.
How long should a stair stringer be?
The stringer runs along the slope, so its length is the hypotenuse of the total run and the total rise. For a 108 inch rise over a 140 inch run that is about 177 inches. Add a little extra at each end for the cut to the floor and the connection at the top.
What are the code limits for risers and treads?
Most residential code (IRC) caps the riser at 7.75 inches and asks for a tread depth of at least 10 inches, with every step within 3/8 inch of the others. The calculator checks your riser and tread against those limits, but confirm with your local building department before cutting.
Does the tread nosing change the numbers?
The nosing is the lip that overhangs the step below. It adds to the width of the tread board you cut but not to the total run, since the run is measured riser to riser. Set it to match your boards, commonly around an inch.

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