Calculate stair stringer details: number of risers, exact riser height, treads, and stringer length.
Code check
Material
Usage Tip
Keep every riser equal; even a small variation between steps is a trip hazard and often a code violation.
treads = risers − 1, run = treads × 10
stringer = √(rise² + run²)
Run assumes a 10 inch tread depth; the stringer length is the diagonal to cut.
How to calculate stair stringers
Start with the total rise — the vertical distance from the lower finished floor to the upper one. Divide it by a comfortable riser height (around 7-1/2 in) and round to a whole number of risers; that is your step count. The actual riser is the total rise divided by that number. Multiply the tread depth by the number of treads (one fewer than the risers) to get the total run, and the stringer length is the diagonal across that rise and run. This calculator does all of it, checks your numbers against common code limits, draws the staircase, and lays out the sawtooth cut on a 2x12.
Standard stair rise and run
Comfortable, code-typical stairs cluster around a narrow band. These are common residential guidelines — always confirm your local code, since this tool is a planning aid, not code enforcement.
| Measure | Typical residential guideline |
|---|---|
| Maximum riser height | 7-3/4 in |
| Minimum tread depth | 10 in |
| Minimum stair width | 36 in |
| Comfort rule | 2 x riser + tread = 24 to 25 in |
| Max riser-to-riser variation | 3/8 in |
Deck stair stringer spacing
Stringers carry the load, so wider stairs need more of them. The common rule is a stringer no more than 16 in on center; for heavy traffic or thinner treads, drop to 12 in. Outdoor deck stairs often use deeper treads (two 2x6 boards, about 11 in) and pressure-treated 2x12 stringers.
How many stringers do I need?
Take the stair width and divide by the spacing, then add one. At 16 in on center:
| Stair width | Stringers (16 in OC) |
|---|---|
| 36 in | 3 |
| 48 in | 4 |
| 60 in | 5 |
| 72 in | 6 |
Stair stringer size chart
Stringers are almost always cut from 2x12 stock, which leaves enough material behind the notches to stay strong. Pick a board at least as long as the diagonal stringer length:
| Total run | Approx stringer length | 2x12 board |
|---|---|---|
| up to ~40 in | up to ~55 in | 2x12 x 8 ft |
| up to ~60 in | up to ~80 in | 2x12 x 10 ft |
| up to ~85 in | up to ~110 in | 2x12 x 12 ft |
| longer | longer | 2x12 x 16 ft |
Frequently asked questions
How do I figure out the number of stairs?
Divide the total rise by about 7-1/2 in and round to a whole number. That is the number of risers; treads are one fewer.
What is the maximum riser height?
Commonly 7-3/4 in for residential stairs. Keep every riser within 3/8 in of the others so the stairs feel even underfoot.
What is the minimum tread depth?
Usually 10 in for the part you step on, not counting nosing. Deck stairs often use about 11 in.
How many stringers for a 4 ft wide stair?
Four stringers at 16 in on center. Go to five at 12 in spacing for heavy use or thinner treads.
What size lumber for stair stringers?
2x12 is standard; it leaves enough wood behind the notches. Use pressure-treated 2x12 outdoors.
What is the 2R plus T rule?
Two times the riser plus the tread should fall between 24 and 25 in. It keeps the stairs comfortable to climb.
Deck Calculator · Concrete Calculator · Lumber Calculator · Fence Calculator · Plywood Sheet Calculator
Coming soon: Stair Railing Calculator
This calculator is a planning aid, not code enforcement. Building codes for rise, run, width, nosing, headroom and landings vary by jurisdiction and occupancy; confirm requirements with your local building department and verify every measurement before cutting.