Stair Stringer Calculator
Riser count, riser height, run, and stringers from total rise.
Vertical distance from lower surface to upper surface.
10 in minimum per code; 10.5 to 11 is comfortable.
You need
6 risers
Equal risers at or under the 7 3/4 in code maximum.
- Exact riser height
- 7.50 in
- Treads to cut
- 5 treads
- Total run
- 4.38 ft
- Stringers (16 in oc)
- 4 stringers
- Stringer length (approx)
- 5.8 ft
Estimates only. Verify quantities before ordering.
How this is calculated
Risers = total rise / 7.75 in, rounded up. Riser height = total rise / risers. Treads = risers - 1 (the top surface is the deck or floor). Total run = treads x tread run. Stringers assume 16 in on center across the stair width. Stringer length is the diagonal of rise and run.
Measure the total rise (the vertical distance from the lower landing surface to the upper floor or deck surface) and this calculator lays out the stair: how many steps, the exact height of each riser, the total horizontal run, and how many 2x12 stringers to cut. It divides the rise by the code maximum riser of 7 3/4 inches and rounds up, which yields equal risers at or under the limit.
Equal risers are the entire game in stair building. Code allows no more than 3/8 inch variation between the tallest and shortest riser on a flight, because uneven steps trip people. That is why you calculate from the total rise and divide evenly rather than framing steps one at a time.
Stair layouts for common deck heights
Rows use a 10.5 in tread run and a 36 in wide stair.
| Total rise | Risers | Riser height | Total run |
|---|---|---|---|
| 24 in (low deck) | 4 risers | 6.00 in | 2.63 ft |
| 36 in | 5 risers | 7.20 in | 3.50 ft |
| 45 in | 6 risers | 7.50 in | 4.38 ft |
| 60 in | 8 risers | 7.50 in | 6.13 ft |
| 108 in (full story) | 14 risers | 7.71 in | 11.38 ft |
Common questions
What is the maximum riser height by code?
The IRC allows risers up to 7 3/4 inches and treads at least 10 inches deep, with no more than 3/8 inch variation between risers in a flight. Some jurisdictions are stricter. Comfortable stairs usually land around a 7 inch riser with a 10 1/2 to 11 inch run.
How do I measure total rise correctly?
Measure vertically from the finished surface you will stand on at the bottom to the finished surface at the top, at the exact spot the stair will land. Sloped ground matters: a landing spot 6 feet out can be inches lower or higher than at the deck, and the stair must be figured at its landing point.
What lumber do stringers use?
2x12s, because cutting a 7 in riser and 10 1/2 in tread notch out of anything narrower leaves too little uncut wood. The rule of thumb is at least 5 inches of solid material behind the notches, sometimes 3.5 in throat is cited minimal; verify locally. Use pressure-treated 2x12 outdoors and crown all stringers the same way.
How many stringers does a stair need?
Space stringers no more than 16 inches on center for 2x lumber treads, so a 36 inch wide stair takes three and a 48 inch stair takes four. Composite treads usually require closer spacing, often 12 inches or less, so check the decking manufacturer's span chart.