Common flights
| Flight | Rise | Risers | Riser | Treads | Tread | Run | Stringer |
|---|---|---|---|---|---|---|---|
| Deck, 3 steps | 21" | 3 | 7" | 2 | 11" | 1' 10" | 2' 6 7/16" |
| Porch, 30 inches | 30" | 4 | 7 1/2" | 3 | 11" | 2' 9" | 3' 8 5/8" |
| Basement, 8 foot | 8' 1" | 14 | 6 15/16" | 13 | 10" | 10' 10" | 13' 6 3/16" |
| Between floors | 9' 1 3/4" | 16 | 6 7/8" | 15 | 10" | 12' 6" | 15' 5 7/8" |
How this is worked out
The total rise is the one number you can't change, so everything starts there. The calculator divides it by your target riser, tries the whole numbers of steps on either side, and keeps the one whose riser lands closest to the target. On a tie it takes more steps, which gives the shorter riser. Then it divides the rise by that count, exactly, for the riser you'll actually build.
Every input is rounded to the nearest sixteenth first, the way Handyman Calc does it. The riser stays an exact fraction, and each stringer mark is rounded from the exact running total rather than by adding up rounded risers, so the last mark is the floor. The stringer length and angle come from the rise and the run, and the stringer is rounded once, to the nearest sixteenth.
The limits it checks are the International Residential Code's for homes, section R311.7.5: a riser of 7 3/4" or less and a tread of 10" or more. Decks, garages and other jurisdictions can have their own numbers, so treat the check as a reminder and look up your local code. For the usual rises already worked out, there's a stair riser chart with a PDF to print.
On your phone, on the job site
On a phone, Handyman Calc has this stair screen, with the same exact fractions, and fourteen more calculators for decks, roofs, drywall and concrete. It works with no signal, and it's free.
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Charts worked out with the same math:
- how many bags of concrete a slab takes
- how many sheets of drywall a room takes
- a fraction to decimal chart for inches
- how much paint a room takes
- how much mulch a bed takes
- a roof pitch chart
- how many steps a rise takes
- the diagonal that squares a frame
- board feet for common lumber
More calculators:
Frequently asked questions
How do you calculate stairs?
Measure the total rise, floor to finished floor. Divide it by about 7" and round to a whole number of steps: that's the riser count. Divide the rise by that count for the exact riser height. Treads are one fewer than risers, and the total run is treads times tread depth.
How many steps do I need for a 9 foot ceiling?
It depends on the floor-to-floor rise, not the ceiling. A typical 9' ceiling with a 10" floor system is about 118" of rise, which is 17 risers at 6 15/16" and 16 treads. Measure your own rise and type it in.
Why is there one fewer tread than risers?
The top riser lands on the upper floor, and that floor is the last tread. Count them equal and you buy one tread too many.
What is the maximum riser height?
7 3/4" in a home under the International Residential Code (R311.7.5), with treads at least 10" deep. Local codes can change these numbers, so the calculator reports them and doesn't stop you.
How long is a stair stringer?
The square root of rise squared plus run squared. 56" of rise over 7 treads of 10" is a 70" run and a stringer of 7' 5 5/8". Buy the board longer than that so you can cut the top and bottom plumb and level.
Why mark the stringer from the list and not add the riser each time?
Because the riser is rarely a clean sixteenth. 109 3/4" over seven risers is 15 19/28" each. Round that and add it seven times, and the top step ends 1/16" off the floor. The marks here are each rounded from the exact total, so the last one lands on it.