Stair Stringer Calculator
with a Cut Sheet
Enter your floor-to-floor rise. Get the riser and tread layout, your framing square settings, a cut list and a drawing of the stringer to scale.
Scale drawing · Code checks · Works on your phone
For reference only. Check riser, tread, throat and headroom against your local code, and test-fit one stringer before cutting the rest.
How to use the stair stringer calculator
- 1
Measure the total rise
Measure from the finished lower floor to the finished upper floor, and take it at the actual stair location, since floors aren't always level.
- 2
Set your target
Enter the riser height you'd like and your tread depth. The calculator rounds to a whole number of risers, then divides the rise evenly between them.
- 3
Mark and cut
Set your framing square to the unit rise and unit run in the cut sheet, and cut one stringer first to test-fit it.
How stair stringers are calculated
Risers = total rise ÷ target riser height, rounded to a whole number
Unit rise = total rise ÷ risers
Treads = risers − 1, because the top riser lands on the upper floor
Total run = treads × tread depth
Stringer length = √(total rise² + total run²)
For example, a 9' rise with a 7 1/4" target gives 15 risers at 7 3/16" each. With 10 1/2" treads, that's 14 treads, a total run of 12' 3" and a stringer length of 15' 2 7/16", which you'd cut from 16' stock.
What it checks and what it doesn't
These are the common residential limits, based on the 2018 International Residential Code (IRC). The calculator only flags the first two. Your local code may differ, so check it before you build.
| Item | Limit | Flagged here? |
|---|---|---|
| Riser height | No more than 7 3/4" | Yes |
| Tread depth | At least 10" | Yes |
| Nosing | 3/4" to 1 1/4" where treads are under 11" | No |
| Stair width | At least 36" | No |
| Headroom | At least 6' 8" | No |
Check nosing, width and headroom yourself. The calculator also won't tell you when a flight is tall enough to need a landing, which is at about 12 feet of rise depending on your code.
It does flag three things that aren't in the table: a riser under 4", and two rules of thumb that aren't code. Those are 2R+T (two risers plus one tread) between 24" and 25" for a comfortable stair, and at least 5" of throat, which is the wood left behind each notch.
Why the top and bottom cuts are different
Once treads are on, the first step would be too tall and the last too short if every notch were the same. So the bottom of the stringer is cut shorter by one tread thickness, which is called dropping the stringer, and the top riser ends up taller by the same amount. Every finished step then matches the unit rise. This assumes the floors at both ends are finished, so adjust if flooring is still to come.
Questions
- Three is common for a 36" wide stair, but it depends on your tread material and local code. Wider stairs or thinner treads need more.
- Use a 2x12 for most stairs. Cutting the notches removes a lot of wood, and a 2x10 can leave less than the 5" of throat that's commonly used as a minimum. The calculator warns you if that happens.
- It's the wood left between the inside corner of a notch and the back edge of the board. That's the part carrying the load, so it can't be cut too thin.
- The layout works the same way, but measure the rise from the deck surface to the finished landing, and check your local deck code, since exterior stairs can have their own requirements.
More free tools
Keep these next to your quotes
QuoTrak's Field Tools are on the Free plan, along with unlimited quotes and invoices and live margin on every job. No credit card.