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Stair Calculator
Enter the total rise from one floor to the next and the calculator divides it into equal risers, then gives the riser height, number of treads, total run, stringer length and stair angle. It also flags a layout outside the common residential code limits.
- Number of risers
- 15
- Number of treads
- 14
- Total run
- 140 in
- Stringer length
- 176.82 in
- Stair angle
- 37.65 °
- Code check
- Within IRC limits (riser ≤ 7¾ in, tread ≥ 10 in)
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Measure the total rise from finished floor to finished floor.
- Enter the tallest riser you are willing to have.
- Enter the tread run you plan to use.
- Check the riser height, total run and the code check line.
Worked examples
A 108 in floor-to-floor rise with risers no taller than 7½ in and 10 in treads
- Number of risers
- 15
- Riser height
- 7.2 in
- Number of treads
- 14
- Total run
- 140 in
- Stringer length
- 176.82 in
- Stair angle
- 37.65 °
- Code check
- Within IRC limits (riser ≤ 7¾ in, tread ≥ 10 in)
Deck stairs with a 57 in rise, 7¾ in maximum riser and 10½ in treads
- Number of risers
- 8
- Riser height
- 7.125 in
- Number of treads
- 7
- Total run
- 73.5 in
- Stringer length
- 93.01 in
Code limits
The International Residential Code (IRC) figures used here are a maximum riser height of 7¾ in and a minimum tread depth of 10 in. The IRC also limits the variation between the tallest and shortest riser in a flight to ⅜ in, which is why the rise is divided into equal steps.
These are IRC figures and local code governs: some jurisdictions use different limits, and commercial stairs follow stricter rules. These figures are planning estimates. Local building codes and a qualified professional govern the actual design.
Comfort and layout
A long-standing carpenter’s rule is that two risers plus one tread should come to 24–25 in. Risers of 7–7½ in with 10–11 in treads feel comfortable to most people.
The top tread is normally the upper floor itself, so there is one fewer tread than risers. The stringer length here is the diagonal between the two ends of the flight; buy stock a little longer to allow for the end cuts.
Questions people ask
How many steps do I need for a 9 ft rise?
A 108 in rise with risers no taller than 7½ in needs 15 risers of 7.2 in each and 14 treads. With 10 in treads the stairs run 140 in (11 ft 8 in) horizontally.
What is the maximum riser height for stairs?
7¾ in under the International Residential Code, with a minimum tread depth of 10 in. Check your local code, which may differ.
How long a stringer do I need?
The square root of rise² plus run². For a 108 in rise and 140 in run that is 176.8 in, about 14 ft 9 in, so a 16 ft board.