CalcArcade.

Stair Calculator

Enter the total height from floor to floor, the riser height you would like and the tread depth. The calculator gives the number of steps, an even riser height, the total run, the stringer length and the angle.

Your numbers

Result

How we calculate it

The number of risers is the total rise divided by the riser height you want, rounded to a whole number. The actual riser height is the total rise divided by that number, so every step is the same. There is one tread fewer than risers, because the top floor acts as the last tread.

The total run is the number of treads times the tread depth. The stringer length is the diagonal, √(total rise² + total run²), and the angle is the arctangent of riser ÷ tread. A rise of 105 inches with a 7 inch riser and a 10 inch tread gives 15 risers, 14 treads, a run of 140 inches (11 ft 8 in), a stringer of 175 inches (14 ft 7 in) and an angle of 35°.

Assumptions and limits

  • The International Residential Code, used in much of the United States, allows a riser of up to 7 3/4 inches and needs a tread of at least 10 inches. The calculator warns you if you go outside those. Your local building code governs, so check it.
  • The stringer length is the diagonal length of the cut line. A real stringer needs a longer board to leave room for the cuts.
  • Treads often overhang the riser with a nosing, which is not counted here. Use the code rules for headroom, width and handrails as well.

Frequently asked questions

How do I calculate the number of steps in a staircase?

Divide the total rise by the riser height you want and round to the nearest whole number. Then divide the total rise by that number to get the actual, equal riser height.

What is the maximum riser height?

The International Residential Code allows up to 7 3/4 inches, and many places have a similar limit. Your local code is the one that counts.

Why is there one fewer tread than risers?

The floor at the top of the stairs takes the place of the last tread, so a staircase with 15 risers has 14 treads.

Related calculators

Worked example (a fixed example using the starting numbers, it does not change as you type)

Inputs: Total rise from floor to floor (inches) = 105; Riser height you want (inches) = 7; Tread depth (inches) = 10.

  • Number of risers 15
  • Riser height 7.000 in
  • Number of treads 14
  • Total run 140.00 in
  • Stringer length 175.00 in
  • Stair angle 35.0 degrees
  • Total run (feet and inches) 11 ft 8 in
  • Stringer length (feet and inches) 14 ft 7 in

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Last reviewed: . Formulas and assumptions are described on our methodology page. For information only; not professional advice.