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Stair Stringer Calculator · Free calculator

Stair Stringer Calculator: 120" Total Rise

For 120" from finished floor to finished floor (10' 0"), you need 16 risers of 7-1/2" and 15 treads. With 10" treads the stairs run 12' 6" and each stringer is 16' 0-1/16" long — cut from a 18' 2x12.

Quick answer

Risers
16 × 7-1/2"
Treads (10")
15
Total run
12' 6"
Stringer length
16' 0-1/16"
2x12 stringers (36" wide)
3 × 18'
IRC
✓ Meets code

▍Stair Stringer Calculator

in
Tread depth (run)
in
Risers × height
16 × 7-1/2"
✓ Meets IRC (riser ≤ 7-3/4", tread ≥ 10")
10' 0"RUN 12' 6"
Treads
15
Total run
12' 6"
Stringer length
16' 0-1/16"
Angle
36.9°
2x12 stringers
3 × 18'
2R + T
25.00in

120" rise — tread depth options

TreadTotal runStringerAngle2R + TStock
10"12' 6"16' 0-1/16"36.9°25.0018'
10-1/2"13' 1-1/2"16' 6"35.5°25.5018'
11"13' 9"17' 0"34.3°26.0020'
1' 0"15' 0"18' 0-5/16"32.0°27.0020'

120" 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
158"14No — too tall
167-1/2"15Yes
177-1/16"16Yes
186-11/16"17Yes

How the math works

  1. Risers = 120" ÷ 7.75" max = 15.48 → round up to 16
  2. Riser height = 120" ÷ 16 = 7.5000" ≈ 7-1/2"
  3. Treads = risers − 1 = 15
  4. Total run = 15 × 10" = 12' 6"
  5. Stringer = √(120² + 150.0²) = 16' 0-1/16"

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 120" 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 120 inch rise?

16 risers (steps up) of 7-1/2" each, with 15 treads. That stays under the IRC maximum riser height of 7-3/4".

How long of a stringer do I need for a 120" rise?

16' 0-1/16" along the slope with 10" treads (total run 12' 6"). Buy 18' 2x12s to leave room for the top and bottom cuts.

What is the riser height for a 120" stair?

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

What angle are 120" stairs?

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