Stair Stringer for 18" Rise: 3 Steps × 6"

Tread	Total run	Stringer	Angle	2R + T	Stock
10"	1' 8"	2' 2-15/16"	31.0°	22.00	8'
10-1/2"	1' 9"	2' 3-11/16"	29.7°	22.50	8'
11"	1' 10"	2' 4-7/16"	28.6°	23.00	8'
1' 0"	2' 0"	2' 6"	26.6°	24.00	8'

Tread

Total run

Stringer

Angle

2R + T

Stock

10"

1' 8"

2' 2-15/16"

31.0°

22.00

10-1/2"

1' 9"

2' 3-11/16"

29.7°

22.50

11"

1' 10"

2' 4-7/16"

28.6°

23.00

1' 0"

2' 0"

2' 6"

26.6°

24.00

Risers	Riser height	Treads	Meets IRC
2	9"	1	No — too tall
3	6"	2	Yes
4	4-1/2"	3	Yes
5	3-5/8"	4	Yes

Risers

Riser height

Treads

Meets IRC

No — too tall

Yes

4-1/2"

Yes

3-5/8"

Yes

How the math works

Risers = 18" ÷ 7.75" max = 2.32 → round up to 3
Riser height = 18" ÷ 3 = 6.0000" ≈ 6"
Treads = risers − 1 = 2
Total run = 2 × 10" = 1' 8"
Stringer = √(18² + 20.0²) = 2' 2-15/16"

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 18" 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 18 inch rise?

3 risers (steps up) of 6" each, with 2 treads. That stays under the IRC maximum riser height of 7-3/4".

How long of a stringer do I need for a 18" rise?

2' 2-15/16" along the slope with 10" treads (total run 1' 8"). Buy 8' 2x12s to leave room for the top and bottom cuts.

What is the riser height for a 18" stair?

6.000" — about 6" on the tape. 2R + T = 22.00", outside the 24"–25" comfort range — consider adjusting tread depth.

What angle are 18" stairs?

31.0° with 10" treads. Residential stairs typically fall between 30° and 37°.

Stair Stringer Calculator: 18" Total Rise

Quick answer

▍Stair Stringer Calculator

18" rise — tread depth options

18" rise — riser count options