Skip to content
SiteSumGet the app

Free stair calculator · worked by SiteSum’s engine

Stairs, to the sixteenth.

Floor to floor in, the whole flight out: risers, treads, run, stringer and angle. Change a number and the drawing follows.

Reads as 9' 0"

Reads as 7-3/4"

Reads as 10"

Type it the way it reads on the tape: 9' 2-1/4", 7 3/4 or 2400mm. A bare number is inches. 7-3/4" and 10" are reference limits, not your local code.

14 risers at ≈ 7-11/16"

Risers
14
Riser height
≈ 7-11/16"
Treads
13
Total run
10' 10"
Stringer
≈ 14' 1"
Angle
37.65°

Cut all 14 risers to the 7-11/16" mark and the flight ends 3/8" short. Lay the stringer out from the exact height, not the rounded one.

≈ 14' 1"9' 0"10' 10"≈7-11/16"

The same engine, in your pocket

On site, with no signal.

This page runs the math from SiteSum, a feet-inch calculator for iPhone with ten builders like this one. It works offline, prints every answer to a paper tape and exports the job as a PDF. Pro is $24.99, once.

Download on the App Store

How it’s worked

  • Risers = total rise ÷ max riser, rounded up to a whole step.
  • Riser height = total rise ÷ risers, so every step is the same.
  • Treads = risers − 1. The upper floor is the last step.
  • Total run = treads × tread depth.
  • Stringer = √(rise² + run²), the straight line from the foot of the first riser to the top.
  • Angle comes from riser height over tread depth.

Answers are given to the nearest sixteenth. When the exact answer falls between marks, it starts with ≈ so you know it was rounded.

Where do I measure the total rise?

From the finished floor at the bottom to the finished floor at the top. If the flooring isn’t down yet, add its thickness at the top and take it off at the bottom, or the first and last steps come out a different height from the rest.

Why one fewer tread than risers?

You step up a riser, onto a tread, and so on. After the last riser you’re standing on the upper floor, which takes the place of a tread.

What does ≈ mean on the riser height?

The exact height falls between two sixteenths. If you cut every riser to the rounded mark, the small difference adds up over the flight, which is why the calculator tells you how far it would be out. Lay the stringer out from the exact height.

Are 7-3/4" and 10" the code?

They are the limits most US residential codes use for the tallest riser and the shallowest tread, and they are a starting point only. Check your local code: the inspector has the last word.

How long a board do I need for the stringer?

Longer than the stringer length shown. That figure is the line of the flight; the plumb cut at the top and the level cut at the foot need extra board at each end.

More free calculators