Stair calculator

Find the number of risers, riser height and tread depth for comfortable stairs that fit the code.

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Letters on the drawing match the letters next to the inputs.
in
in
More settings
in
in
Risers14 pcs
Riser height7.71 in

Shopping list

  • Treads13 pcs
  • Total run10.8 ft
  • Stringer length14.1 ft

How we got there

Tread depth
10 in
Stair angle
37.6 °
Stride: 2 risers + tread
25.4 in

Results are estimates. Always check the coverage printed on the product and your local building code.

How it is calculated

The total rise is divided by the preferred riser height and rounded to a whole number of risers. Tread depth follows the stride rule (two risers plus one tread about 25 in), but never less than the minimum tread you set. The upper floor is the top step, so there is one tread fewer than risers. The defaults follow the IRC for homes: risers up to 7 3/4 in and treads at least 10 in.

FormulaRisers = total rise ÷ preferred riser, roundedComfortable stride: 2 × riser + tread ≈ 24–26 inAngle = arctan(riser ÷ tread)

Example

With 108 in from floor to floor you get 14 risers of 7.71 in and 13 treads of 10 in. The stair runs 10.8 ft, its angle is 37.6° and each stringer is about 14.1 ft long.

Tips from practice

  • Riser heights may not vary by more than 3/8 in in the same flight.
  • Keep at least 6 ft 8 in of headroom over the stair.
  • Stringers are usually cut from 2×12 lumber.

Questions and answers

What is the maximum riser height?

The IRC allows up to 7 3/4 in for homes, with treads at least 10 in. Local codes may differ.

How many steps for 9 feet?

With 108 in of rise, 14 risers of about 7.7 in.

What if I do not have enough run?

Choose “Fit a given run”. If the stair gets too steep, add a landing or turn.

Found a mistake in a formula? Write to contact@planicalc.com