Stair Calculator
Enter the total rise and your target step size. You get the riser count, exact riser height, stringer length and angle, drawn to scale and checked against the 2021 IRC.
Risers
14× 7 11/16"
- Treads
- 13 × 10"
- Exact riser
- 7.714"
- Total run
- 10′ 10"
- Angle
- 37.6°
- Stringer length
- 14′ 1"
- Buy stringers
- 4 × 16 ft
- Throat left
- 5 1/8"
- Headroom opening
- ≥ 9′ 8 11/16"
- Riser 7.714" ≤ 7¾"
IRC R311.7.5.1: maximum riser height 7¾ in. - Riser ≥ 4"
IRC R311.7.5.1: risers must be at least 4 in. - Tread run 10" ≥ 10"
IRC R311.7.5.2: minimum tread depth 10 in, nosing to nosing. - Nosing 1" between ¾" and 1¼"
IRC R311.7.5.3: nosing required where tread depth is under 11 in with solid risers. - Rise between landings 108.0" ≤ 151"
IRC R311.7.3: a single flight may not rise more than 12 ft 7 in without a landing. - Stair width 36" ≥ 36"
IRC R311.7.1: 36 in clear width above the handrail height. - Stringer throat 5.14" ≥ 3½"
Common framing practice (and many span guides): keep at least 3½ in, ideally 5 in, of solid wood below the notches. - Comfort: 2R + T = 25.43" (aim 24–25")
Blondel's rule of thumb for a natural stride; not a code requirement.
How to lay out a stringer with a framing square
Your stringer, drawn to scale from the numbers above. Step through the four layout steps and watch where the framing square goes.
Clamp stair gauges (or tape) on a framing square: 7 11/16" on the tongue (short leg) for the rise and 10" on the body (long leg) for the run.
How many stairs for your ceiling height
Total rise = ceiling height + floor framing and finish above it. The table assumes a 2×10 floor with ¾″ subfloor and finished flooring (about 10 3/4″ added) and the most even riser at or under 7¾″.
| Ceiling | Total rise | Risers | Riser height | Treads | Total run at 10″ | Total run at 11″ |
|---|---|---|---|---|---|---|
| 8 ft | 8′ 10 3/4" | 14 | 7 5/8" | 13 | 10′ 10" | 11′ 11" |
| 9 ft | 9′ 10 3/4" | 16 | 7 7/16" | 15 | 12′ 6" | 13′ 9" |
| 10 ft | 10′ 10 3/4" | 17 | 7 11/16" | 16 | 13′ 4" | 14′ 8" |
| 12 ft | 12′ 10 3/4" | 20 | 7 3/4" | 19 | 15′ 10" | 17′ 5" |
A 12 ft ceiling gives more than 151″ of rise, so the IRC (R311.7.3) requires a landing part-way up. Deck stairs: total rise is from the deck surface to the landing pad. A 30″ deck needs 4 risers of 7½″; a 48″ deck needs 7 risers of 6 7/8″ (or 6 of 8″, which is over the IRC limit).
How the stair math works
- Risers = total rise ÷ target riser, rounded up. 108" ÷ 7.5" → 14 risers.
- Exact riser = total rise ÷ risers = 7.714" (≈ 7 11/16").
- Treads = risers − 1, because the upper floor is the last step (with a flush-mounted stringer the top tread sits level with the deck, so treads = risers).
- Total run = treads × tread run.
- Stringer length = √(total rise² + total run²).
- Angle = arctan(riser ÷ run).
Measure the total rise at the spot where the stair will land, not at a wall: floors are rarely level, and a 1/2" error spreads over every step. If the finished flooring is not down yet, add its thickness at the top and bottom.
For every code rule in one place, including handrails, guards, headroom and winders, see the IRC stair code checker.
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