Stair Calculator

1. Enter your total rise — the finished-floor-to-finished-floor height the staircase has to climb, measured straight up. For a deck this is the ground to the top of the decking; indoors it is the height between two floors.
2. Enter your total run — the horizontal distance the staircase is allowed to cover from the bottom step to the top, measured along the ground.
3. Read your stair layout instantly: the number of steps, the rise and run of each step, the stringer length, and the stair angle.
4. Open More options to switch to metric (centimeters), set a different ideal step height, or force an exact number of steps.

Every staircase is defined by two measurements: the total rise (how far up it goes) and the total run (how far out it reaches). A stair calculator splits those totals into equal steps. Each step has a rise (its height) and a run, also called the tread depth (how far your foot lands).

The number of vertical faces is the number of *risers*; the number of horizontal boards you actually walk on is the number of *treads*, which is always one fewer than the risers because the upper floor acts as the final tread. Getting a comfortable rise and run for stairs matters more than most people expect — uneven or too-steep steps are a leading cause of trips.

A common target is a 7 to 7.75 inch rise paired with a 10 to 11 inch tread. This tool aims for a 7.5 inch step by default, then rounds to a whole number of steps so every step is identical. The stringer is the sawtooth board that carries the treads; its length is the diagonal from the bottom to the top, which is why the tool also reports the stair angle.

Number of steps (risers) = total rise ÷ ideal step rise, rounded to the nearest whole number

Rise per step = total rise ÷ number of steps

Treads = risers − 1, so run per step = total run ÷ (risers − 1)

Stringer length = √(total rise² + total run²)

Stair angle = arctangent(total rise ÷ total run)

Example: a 60 in rise ÷ 7.5 in ideal = 8 steps. Each step rises 60 ÷ 8 = 7.5 in. With a 105 in total run and 7 treads, each tread is 15 in deep, the stringer is √(60² + 105²) ≈ 120.93 in, and the angle is about 29.7°.

Deck stairs, 60 in rise: You want stairs off a deck that sits 60 inches above the yard, with room for a 105 in run. The calculator returns 8 steps at 7.5 in each, 15 in treads, a 120.93 in stringer, and a 29.7° slope — a comfortable, code-friendly flight.

How many steps for an 8 foot rise: An 8 ft basement-to-first-floor height is 96 in. At a 7.5 in target that is 13 steps (96 ÷ 13 ≈ 7.38 in each). Give it a 132 in run and each of the 12 treads is 11 in deep.

Tight indoor stairwell: With a 108 in rise and only a 96 in run you get 14 steps of 7.71 in and 13 treads of about 7.4 in — steep and cramped, a sign you need more horizontal space or a switchback.

- Keep every step identical. Building codes limit the difference between the tallest and shortest riser in a flight to about 3/8 inch. Rounding to a whole number of steps keeps them even.
- Check the 2R + T rule. A comfortable stair satisfies 2 × rise + tread ≈ 24–25 inches. A 7.5 in rise with a 10 in tread gives 25 — right in the sweet spot.
- Mind the maximum rise. Most US residential codes cap the riser at 7.75 in and require a tread of at least 10 in. If your rise per step comes out above 7.75, add a step in More options.
- Buy the next size up for stringers. A 120.93 in stringer needs a board longer than 10 ft once you account for the plumb and seat cuts — order a 12 ft 2×12.
- Confirm headroom. You need at least 6 ft 8 in of clearance above the stair nosings; a steep angle can create a low spot at the top of the flight.