Stair Calculator
Enter the total rise (the finished floor-to-floor height) and your target tread depth. The calculator chooses a riser count that keeps each step at a comfortable, code-compliant height, then returns the riser height, number of treads, total run, cut-stringer length and the stair angle — and checks it against the IRC residential limits.
Your measurements
Finished floor to finished floor — the full vertical height the stairs climb.
Run of each step (front to back). IRC minimum is 10 in.
Layout
- Number of treads
- 13 treads
- Total run (horizontal)
- 130 in (10.83 ft)
- Stringer length
- 169 in (14.08 ft)
- Stair angle
- 37.6°
Stair layout
14 risers @ 7.71 in
13 treads · 10.8 ft run · 37.6°
Code check
- 2 × riser + tread
- 25.4 in(Comfortable range is 24–25 in)
- Status
- Within IRC limits (riser ≤ 7.75 in, tread ≥ 10 in).
Riser height vs. code max
Estimates only. Verify against your supplier's coverage figures before ordering.
The formula
Risers = round(total rise ÷ 7.5) · Riser height = total rise ÷ risers · Total run = (risers − 1) × tread · Stringer = √(rise² + run²)
Example: A 108-in rise (9 ft) with 10-in treads gives 14 risers at 7.71 in, 13 treads, a 130-in total run, a ~178-in stringer and a 37.6° stair.
How it works
- 1Divide the total rise by a comfortable target riser (~7.5 in) and round to a whole number of risers.
- 2Riser height = total rise ÷ that riser count, so every step is exactly equal (required by code).
- 3There's always one fewer tread than risers — the top riser lands on the finished floor above.
- 4Total run = treads × tread depth; the cut-stringer length is the hypotenuse √(total rise² + total run²).
- 5Check it: the IRC caps residential risers at 7.75 in and sets a 10-in minimum tread, and 2 × riser + tread should land around 24–25 in.
Frequently asked questions
How do I calculate stair rise and run?
Measure the total rise (finished floor to finished floor). Divide by ~7.5 in and round to get the riser count, then divide the total rise by that count for the exact riser height. The run is the tread depth (≥10 in) times the number of treads, which is one fewer than the risers.
What is the maximum stair riser height?
The International Residential Code (IRC) limits residential stair risers to 7.75 inches and requires a minimum tread depth of 10 inches. Risers must also be equal to within 3/8 inch across the whole flight.
How long does a stair stringer need to be?
The cut stringer follows the diagonal of the stairs, so its length is the square root of (total rise² + total run²). For a 108-in rise and 130-in run that's about 169 in along the slope — buy a 2×12 a bit longer to allow for the cuts.
How many stringers do I need?
Use a stringer at each side plus one in the middle for stairs up to 36 in wide; add another for every additional ~16 in of width, or follow the tread manufacturer's span rating for composite and pre-cut treads.