Stair Calculator

The total rise is the height from the finished floor at the bottom to the finished floor at the top, and the building fixes it. It sets how many risers you need and how tall each one is. The tread depth you choose sets how far the stairs reach across the floor. Once the plan works, the stringer layout and cuts come next.

How to use this calculator

1. Take the total rise with a tape, from the finished surface at the bottom to the finished surface at the top. Add the thickness of any flooring still to go down.
2. Enter the rise in the unit you measured in, after two readings taken near the stair agree.
3. Set the tallest riser you will accept. The starting value is the code maximum of 7.75 inches. A lower value gives a gentler climb with more steps and a longer run.
4. Choose the tread depth. The minimum is 10 inches. A deeper tread adds foot room, and it also adds to the total run.
5. Read the risers, riser height, total run and stair angle. A larger stair angle means a steeper flight.

Worked examples

Total run of the flight at typical floor-to-floor heights and tread depths

Each cell: Total run (in). Inputs not in the table use the calculator's starting values.

Measuring the total rise

Use the surface you will walk on at each end, not the subfloor. If the stairs rise through an opening, drop a tape or a plumb line through it and read the height from the finished floor below.

One small error in this figure carries into every riser, so measure twice before you cut.

Why every riser must match

Every riser should be the same height. People climb by feel, so one riser that is taller or shorter than the rest is the step most likely to catch a foot. The calculator splits the rise into equal risers. Cut every riser to the riser height it shows.

The residential code caps the difference between the largest and smallest riser in a flight at 0.375 inch, and the same cap applies to treads. Risers cut to one height differ by nothing, so the cap is met by design. Small errors still add up from step to step, so check that the risers sum to the total rise.

Fitting the run into the room

The top riser sits on the upper floor and covers no run of its own, so the total run is the treads times the tread depth. For a straight flight, the riser limit and the tread minimum set the shortest run the code allows for a given rise. If the room cannot hold that run, move the stairs or add a turn at a landing, because a shallower tread is not an option.

Check the stair width and the headroom. The stair must be at least 36 inches wide, and headroom must be at least 80 inches, measured under the lowest beam, duct or light fixture above the treads.

Outdoor steps off a deck or porch are measured from the decking, so the deck step calculator is the better fit. Where a gentler slope matters more than floor space, a ramp trades the steps for a longer, flatter surface.

Code check before you build

Use this list before you order lumber. Local codes can be stricter or differ in other ways, and the inspector has the final word.

• Riser height no taller than 7.75 inches.
• Tread depth at least 10 inches.
• Largest difference between risers, or between treads, 0.375 inch or less.
• Stair width at least 36 inches.
• Headroom at least 80 inches.
• Landing at least 36 inches deep for a straight run.
• Handrail on at least one side of any flight with 4 risers or more.
• Handrail height of 34 to 38 inches above the nosings.

Stair parts and terms: rise, run, riser, tread, nosing and stringer

The total rise is the height between finished floors. The total run is the flat distance the stairs cover. A riser is the upright part of a step, and a tread is the part you stand on. The nosing is the edge of the tread that overhangs the riser below, and the stringer is the sloped board that carries the treads.

Planning stairs with a landing or a turn

Stairs with a landing are two flights. Split the total rise between them, run the calculator once for each flight, and keep every riser the same height in both. A landing must be at least as wide as the stairs and, on a straight run, at least 36 inches deep. If you use winders, each tread needs at least 10 inches of depth at the walkline and at least 6 inches everywhere across it.

What size stringer do I need, and how many?

A stringer is the sloped board that carries the treads, and its length comes from the total rise and run in the calculator. For deck stairs, the American Wood Council's deck guide calls for cut stringers from 2x12 lumber, at least 3 stringers of them, spaced no more than 18 inches apart.

Common questions