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Stair Stringer Calculator · Free calculator

Stair Stringer Calculator: 30" Total Rise

For 30" from finished floor to finished floor (2' 6"), you need 4 risers of 7-1/2" and 3 treads. With 10" treads the stairs run 2' 6" and each stringer is 3' 6-7/16" long — cut from a 8' 2x12.

Quick answer

Risers
4 × 7-1/2"
Treads (10")
3
Total run
2' 6"
Stringer length
3' 6-7/16"
2x12 stringers (36" wide)
3 × 8'
IRC
✓ Meets code

▍Stair Stringer Calculator

in
Tread depth (run)
in
Risers × height
4 × 7-1/2"
✓ Meets IRC (riser ≤ 7-3/4", tread ≥ 10")
2' 6"RUN 2' 6"
Treads
3
Total run
2' 6"
Stringer length
3' 6-7/16"
Angle
36.9°
2x12 stringers
3 × 8'
2R + T
25.00in

30" rise — tread depth options

TreadTotal runStringerAngle2R + TStock
10"2' 6"3' 6-7/16"36.9°25.008'
10-1/2"2' 7-1/2"3' 7-1/2"35.5°25.508'
11"2' 9"3' 8-5/8"34.3°26.008'
1' 0"3' 0"3' 10-7/8"32.0°27.008'

30" rise — riser count options

IRC R311.7.5.1: riser height 7-3/4" max. Comfortable stairs land at 7"–7-1/2".

RisersRiser heightTreadsMeets IRC
310"2No — too tall
47-1/2"3Yes
56"4Yes
65"5Yes

How the math works

  1. Risers = 30" ÷ 7.75" max = 3.87 → round up to 4
  2. Riser height = 30" ÷ 4 = 7.5000" ≈ 7-1/2"
  3. Treads = risers − 1 = 3
  4. Total run = 3 × 10" = 2' 6"
  5. Stringer = √(30² + 30.0²) = 3' 6-7/16"

Subtract one tread thickness from the bottom riser of the stringer (drop the stringer) so the first step matches the rest.

Trade pro tips

  • Measure the 30" rise from finished floor to finished floor — add flooring and tread thickness to rough measurements.
  • Cut one stringer, test it in place, then trace it for the rest.
  • At 36" wide, use 3 stringers; at wider than 36", add one stringer per 16"–18".

Frequently asked questions

How many steps for a 30 inch rise?

4 risers (steps up) of 7-1/2" each, with 3 treads. That stays under the IRC maximum riser height of 7-3/4".

How long of a stringer do I need for a 30" rise?

3' 6-7/16" along the slope with 10" treads (total run 2' 6"). Buy 8' 2x12s to leave room for the top and bottom cuts.

What is the riser height for a 30" stair?

7.500" — about 7-1/2" on the tape. 2R + T = 25.00", right in the comfortable range.

What angle are 30" stairs?

36.9° with 10" treads. Residential stairs typically fall between 30° and 37°.