Stair Stringer Calculator
Enter your total rise and get the exact riser height, tread count, stringer length, and stair angle, with automatic checks against typical residential code limits.
Floor to floor, or deck surface to grade.
7 to 7.5 is comfortable. Code max is 7.75.
Code minimum is 10 inches.
Number of risers
14
Riser height
7.143 in
Number of treads
13
Total run
136.5 in
Stringer length
169.21 in
Stair angle
36.2 deg
Layout: cut 13 treads at 10.5 in and 14 risers at 7.143 in. Buy stringer stock at least 15 ft long.
How the math works
The calculator divides your total rise by the target riser height and rounds up, which guarantees every riser comes in at or under your target and the code maximum of 7.75 inches. Dividing the rise by that whole number of risers gives the exact height to mark on your framing square.
There is always one fewer tread than risers, because the top step is the deck or floor itself. Total run is treads times tread depth, and the stringer is the hypotenuse of the rise/run triangle, which tells you the minimum board length to buy.
FAQ
- How do I calculate stair stringers?
- Divide the total rise by your target riser height (7 to 7.5 inches is comfortable) and round up to get the number of risers. Divide total rise by that number for the exact riser height. Treads equal risers minus one, and stringer length is the square root of rise squared plus run squared.
- What is the maximum riser height by code?
- The IRC residential code allows a maximum riser height of 7.75 inches and a minimum tread depth of 10 inches. Riser heights within a flight cannot vary by more than 3/8 inch. Always confirm with your local building department.
- How many stringers do I need?
- A common rule is one stringer every 16 inches of stair width. A 36 inch wide stair typically uses three stringers. Composite treads and thinner tread stock often require 12 inch spacing, meaning four stringers.
- What size lumber do I use for stringers?
- Use 2x12s for cut stringers. Cutting the notches removes a large portion of the board, and a 2x12 is the smallest size that leaves enough solid wood (at least 5 inches) below the notches for strength.