Skip to content
BuildMath

Stair Stringer Calculator · Free calculator

Stair Stringer Calculator

Enter the total rise (finished floor to finished floor) and tread depth. You get the number of steps, exact riser height, total run, stringer length and the 2x12 to buy — checked against IRC limits.

Quick answer

IRC max riser
7-3/4"
IRC min tread
10"
Comfort rule
2R + T ≈ 25"
Min width
36"

▍Stair Stringer Calculator

in
Tread depth (run)
in
Risers × height
7 × 6-7/8"
✓ Meets IRC (riser ≤ 7-3/4", tread ≥ 10")
4' 0"RUN 5' 0"
Treads
6
Total run
5' 0"
Stringer length
6' 4-13/16"
Angle
34.4°
2x12 stringers
3 × 8'
2R + T
23.71in

Stair chart by total rise (10" treads)

Total riseRisersRiser heightTreadsTotal runStringer
1' 6"36"21' 8"2' 2-15/16"
2' 0"46"32' 6"3' 2-7/16"
2' 6"47-1/2"32' 6"3' 6-7/16"
3' 0"57-3/16"43' 4"4' 5-13/16"
3' 6"67"54' 2"5' 5-5/16"
4' 0"76-7/8"65' 0"6' 4-13/16"
4' 6"77-11/16"65' 0"6' 8-3/4"
5' 0"87-1/2"75' 10"7' 8-3/16"
6' 0"107-3/16"97' 6"9' 7-1/4"
7' 0"117-5/8"108' 4"10' 10-5/8"
8' 0"137-3/8"1210' 0"12' 9-11/16"
9' 0"147-11/16"1310' 10"14' 1"
10' 0"167-1/2"1512' 6"16' 0-1/16"

How the math works

  1. Risers = total rise ÷ 7.75, rounded up.
  2. Riser height = total rise ÷ risers.
  3. Treads = risers − 1.
  4. Total run = treads × tread depth.
  5. Stringer length = √(rise² + run²).

Trade pro tips

  • Rise is measured finished floor to finished floor.
  • Variation between risers may not exceed 3/8" (IRC).

Frequently asked questions

How do you calculate stair stringers?

Divide total rise by 7.75" and round up for the riser count; divide the rise by that count for riser height; treads = risers − 1; run = treads × tread depth.

What is the code for stair risers and treads?

IRC R311.7.5: max riser 7-3/4", min tread 10" (with nosing), and no more than 3/8" variation between steps.

How many stringers do I need?

Three for a 36" wide stair; add one for every additional 16"–18" of width.

What lumber is used for stair stringers?

Pressure-treated 2x12 for exterior/deck stairs; kiln-dried 2x12 for interior. After cutting, at least 3-1/2" of solid wood should remain below the notches.