Lumber & Stairs
Stair Stringer Calculator
Enter the total rise from the landing surface to the top, your maximum riser, the tread depth and the stair width. We give the cut layout for each stringer.
Worked example
- Risers = 36 in total rise / 7.5 in max riser = 4.8, round up to 5.
- Riser height = 36 / 5 = 7.2 in (7 3/16 in).
- Treads = risers - 1 = 4 (the top step is the floor or deck). Total run = 4 x 10.25 in = 41 in.
- Stringer line = square root of (36^2 + 41^2) = 54.56 in; angle 41.3 degrees.
Common sizes at a glance
| Size | Risers (steps up) | Treads | Total run | Stringer length |
|---|---|---|---|---|
| 24 in total rise | 4 at 6 in | 3 at 10.25 in deep | 2 ft 6 3/4 in | 3 ft 3 in |
| 30 in total rise | 4 at 7 1/2 in | 3 at 10.25 in deep | 2 ft 6 3/4 in | 3 ft 6 15/16 in |
| 36 in total rise | 5 at 7 3/16 in | 4 at 10.25 in deep | 3 ft 5 in | 4 ft 6 9/16 in |
| 48 in total rise | 7 at 6 7/8 in | 6 at 10.25 in deep | 5 ft 1 1/2 in | 6 ft 6 in |
| 60 in total rise | 8 at 7 1/2 in | 7 at 10.25 in deep | 5 ft 11 3/4 in | 7 ft 9 1/2 in |
| 72 in total rise | 10 at 7 3/16 in | 9 at 10.25 in deep | 7 ft 8 1/4 in | 9 ft 9 in |
Measure the rise where the stair will land
For deck and porch steps, measure from the top of the deck surface straight down to where the bottom step will sit. Ground is rarely level, so measure at the landing spot, not at the house.
In the example, a 36 in rise with a 7.5 in maximum riser needs 5 risers at 7 3/16 in and 4 treads of 10.25 in.
Laying out the cuts
Each stringer is a board with a sawtooth of notches. Set a framing square on the board with the riser height on one leg and the tread depth on the other, mark, slide along, and repeat for each step.
Stair gauges, small clamps that lock onto the square, keep every mark the same. One wrong mark repeats on every stringer, so cut one, test it in place, then use it as a pattern.
The bottom step trick
The tread on top of each step adds height. Because the bottom of the stringer sits on the landing with no tread under it, the first riser is usually trimmed by one tread thickness so all steps come out equal.
Skip that step and the first riser ends up taller than the rest, which is easy to trip on.
Boards and stringer count
The calculator gives the stringer length, 4 ft 6 9/16 in for the example, and a board to cut it from: a 2 x 12 at 8 ft. For a 36 in wide stair it shows 4 stringers about 16 in apart, a common layout.
How far apart stringers may be, how much wood must remain behind the notches, and how the stair attaches to the deck are set by code. Your building department and a licensed professional have the final word.
Related parts
Railings on steps usually follow the 4 in sphere rule for openings; the baluster spacing calculator handles that. For the whole outdoor stair, see the deck stairs calculator, and for an indoor flight the stair calculator.
Questions
How many steps for a 30 in deck?
With a 7.5 in maximum riser, 4 risers at 7 1/2 in and 3 treads, per the table on this page.
How long a board for stringers on a 48 in rise?
The stringer line is 6 ft 6 in, so an 8 ft board leaves room for the cuts at each end.
Why is my first step taller than the others?
The bottom of the stringer was not trimmed by the tread thickness. Cut it down by that amount.
How this works: formulas and typical values are listed on our method page; every data source and its license is on sources.
Last reviewed November 2026.