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Generator Hut

Stair Calculator

Risers, treads, total run and stringer length from total rise.

Your measurements

Finished floor to finished floor, measured vertically.

7 to 7.75 in is the usual comfortable range, and most codes cap it near 7.75.

10 in is a common minimum for a main staircase.

Stair dimensions

14risers

14 risers of 7.714 in, 13 treads

Number of risers
14
Actual riser heighttotal rise divided evenly — every riser must match
7.714 in
Number of treadsone fewer than the risers; the top landing is the last step
13
Total run10.83 ft of floor space
130 in
Stringer length169.01 in along the diagonal
14.08 ft
Tread stock needed13 treads at 36 in wide
39 linear ft

Every riser must be the same height. Building codes generally allow only a small variation across a flight — commonly three-eighths of an inch — because an uneven step is the single most reliable way to make people fall.

The actual riser height is total rise divided by a whole number of steps, which is why it rarely matches your target exactly. Adjust the target and watch the step count change to find a combination you like.

Check your local code before cutting. Maximum riser, minimum tread, minimum headroom and handrail requirements all vary by jurisdiction, and stairs are one of the things inspectors reliably measure.

Enter the floor-to-floor rise and a target riser height, and it divides the rise into equal steps and works out the run and stringer length. Every riser in a flight has to match, which is why the actual riser height rarely equals the target you asked for.

Why use this tool?

Equal risers, always

Total rise divided by a whole number of steps. Uneven risers are the single most reliable way to make people fall, and codes police them closely.

Stringer length calculated

The diagonal from the Pythagorean relationship between total rise and total run — the length of timber you actually have to buy.

Run shown in floor space

Total run in both inches and feet, because the question is usually whether the staircase fits the room.

Code figures flagged

Typical maximum riser and minimum tread are stated so you can sanity-check before cutting.

How this stair calculator works

The number of risers is the total rise divided by your target riser height, rounded to the nearest whole number. The actual riser height is then the total rise divided by that count — which is why it comes out at an awkward figure like 7.2 inches rather than the 7.5 you asked for.

Treads are always one fewer than risers, because the top step is the landing itself. Total run is the tread count times the tread depth, and that is the floor space the staircase consumes.

Stringer length is the hypotenuse of the triangle formed by total rise and total run. It is the raw length of timber before the notches are cut, and a little extra at each end is normal for the connections.

How to use it

  1. Step 1: Measure the total rise

    Finished floor to finished floor, measured vertically. This must account for the finished floor thickness at both ends, not the subfloor.

  2. Step 2: Set a target riser

    Seven to seven and three-quarter inches is the comfortable range and near most code maximums. Adjust it and watch the step count change.

  3. Step 3: Choose a tread depth

    Ten inches is a common minimum for a main staircase. Deeper treads are more comfortable but consume more floor space.

  4. Step 4: Check the run fits

    Compare the total run against the space available. If it does not fit, a landing or a winder is needed rather than steeper steps.

Example usage

A standard 9 foot rise
108 inches at a 7.5 inch target gives 14 risers of 7.714 inches each, 13 treads, a total run of 130 inches — just under 11 feet of floor space — and a stringer about 14 feet long.
Adjusting the target
The same 108 inch rise at a 7 inch target gives 15 risers of 7.2 inches and a 140 inch run. More steps, gentler climb, and nearly a foot more floor space consumed.
A deck step
A 24 inch rise at a 7.5 inch target gives 3 risers of 8 inches — over most code maximums. Lower the target to 6 inches and you get 4 risers of 6 inches, which is both safer and legal.

Frequently asked questions

What is a comfortable stair riser height?

Seven to seven and three-quarter inches suits most people, and most residential codes cap the maximum near 7.75. Lower risers are gentler but consume more floor space for the same rise.

Why is the actual riser height different from my target?

Because the total rise has to divide into a whole number of equal steps. Dividing 108 inches by a 7.5 inch target gives 14.4 steps, so the count rounds to 14 and each riser becomes 7.714 inches.

Why is there one fewer tread than riser?

The top step is the upper floor itself, so the last riser rises to the landing and needs no tread. A 14 riser staircase has 13 treads.

How long does a stair stringer need to be?

The diagonal of the rise and run triangle. For a 108 inch rise and 130 inch run that is about 169 inches, or roughly 14 feet, plus a little extra at each end for the connections.

Do stair dimensions have to meet code?

Yes, and stairs are one of the things inspectors reliably measure. Maximum riser, minimum tread, riser consistency across a flight, headroom and handrail requirements all vary by jurisdiction — check locally before cutting timber.

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