Stair Stringer Calculator
Your estimate
- Stringer length
- 14 ft 8 7/8 in14.73 ft · 4.49 m
- Board length to buy
- 16 ft 0 in16 ft · 4.88 m
- Throat (wood left)
- 5 7/16 in5.41 in · 13.7 cm
- Riser height
- 7 3/16 in7.2 in · 18.3 cm
- Treads
- 14
- Total run
- 11 ft 8 in11.67 ft · 3.56 m
- Angle
- 35.75°
- Code check
- OK
Lay out cut stringers for deck and basement stairs: length, board size, throat and how many stringers.
Updated 2026-10-20 · Based on: IRC R311.7 (US) and DIN 18065 (metric).
How to use the Stair Stringer Calculator
- Enter the total rise, target riser and tread depth.
- Enter the stair width and the stringer spacing (18 in on center is common).
- Choose the stringer board width (11¼ in for a 2×12).
- Buy the board length shown and check the throat (at least 3½–5 in).
Formula
Stringer length = √(total rise² + total run²); buy one tread length more for the top and bottom cuts.
Throat = board width − (riser × tread ÷ √(riser² + tread²)). Stringers = width ÷ spacing + 1.
Worked example
With the values preset in the calculator above:
- Total rise
- 9 ft
- Max riser height
- 7.5 in
- Tread depth
- 10 in
- Stair width
- 36 in
- Stringer board width
- 11.25 in
- Stringer spacing
- 18 in
- Stringers
- 3
- Stringer length
- 14 ft 8 7/8 in (14.73 ft)
- Board length to buy
- 16 ft 0 in (16 ft)
- Throat (wood left)
- 5 7/16 in (5.41 in)
- Risers
- 15
Frequently asked questions
How many stringers for a 36 in wide stair?
Three at 18 in on center — 3 with the default spacing. Use 16 in spacing for thin treads.
What size board for stair stringers?
A 2×12 (11¼ in) is standard, leaving enough throat after the notches.
How long a board for 8 steps?
Use the calculator with your rise: the stringer length plus one tread, rounded up to the next standard length (8–20 ft).
More calculators
Estimates only — check quantities with your supplier and local building code before you order.