Stair Stringer Calculator

Riser height, tread run and stringer length for a cut stringer, checked against the IRC 7-3/4 inch riser and 10 inch tread limits

Project Details
Enter your measurements and requirements
Results
Calculated estimates for your project
Number of Risers14
Riser Height7.71"
Number of Treads13
Total Run136.50" (11' 4.5")
Stringer Length174.06" (14' 6.1")
Stair Angle36.3 degrees
Throat Left in a 2x125.03"
IRC Riser and Tread CheckPasses
Materials List
Recommended materials and quantities
Stringers4 cut from 2x12
Board Length16 ft

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Additional Information

About This Stair Stringer Calculator

A stringer is laid out from two numbers: the total rise and the tread run. Divide the rise into equal risers no taller than 7-3/4 inches (IRC R311.7.5.1), give every tread at least 10 inches of run (IRC R311.7.5.2), and the stringer length is the diagonal of the whole flight. This tool does that division for you and returns the exact riser height to mark on your framing square.

Measure the total rise from finished floor to finished floor, including the thickness of the decking or flooring that will go on top. Riser heights in one flight should not vary by more than 3/8 inch, so a sloppy rise measurement shows up as a trip step at the top or bottom.

Building the whole staircase? The stairs calculator prices treads, risers and railings, and the concrete stairs calculator covers poured steps.

How to Use This Calculator
  1. Measure the total rise from the lower finished surface to the upper one, in inches.
  2. Enter the tread run you want; 10 inches is the IRC minimum and 10-1/2 to 11 inches is comfortable.
  3. Leave the max riser at 7.75 inches unless your local code is stricter.
  4. Enter the stair width and stringer spacing to get the stringer count.
  5. Set your stair gauges to the riser height and tread run shown, and mark the first stringer as a pattern.
Frequently Asked Questions

How do I calculate the number of stair risers?

Divide the total rise in inches by 7.75 and round up to the next whole number. Then divide the total rise by that number to get the actual riser height. A 108 inch rise needs 14 risers of about 7.71 inches each.

How many treads does a stringer have?

One fewer than the number of risers, because the top riser lands on the upper floor or deck rather than on a tread. 14 risers means 13 treads.

How long should a stair stringer be?

The stringer length is the hypotenuse of the total rise and total run: the square root of rise squared plus run squared. Buy a board at least a foot longer than that to leave room for the plumb cut at the top and the level cut at the bottom.

What size lumber is used for stair stringers?

Cut stringers are almost always 2x12. Notching for the treads and risers removes a triangle from the board, and the wood left below the notches (the throat) is what carries the load, so a 2x10 rarely leaves enough.

How far apart should stair stringers be?

Many builders space stringers about 16 inches on center for 5/4 decking treads and wider for 2x treads. Check the span rating of your tread material and your local code.

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