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Roofing & Framing

Stair & Stringer Calculator

This stair calculator divides your total rise into equal risers and treads; our deck construction guide covers stairs and guards. Measure the total rise — finished floor to finished floor, or deck surface to the landing below — and the calculator divides it into equal risers no taller than your maximum. It then gives tread count, total run, stair angle and the stringer length to lay out.

Defaults reflect the International Residential Code (R311.7.5): maximum riser 7¾ in and minimum tread 10 in. New York City enforces its own building code, and other jurisdictions may amend these limits — check yours.

Results from this stair calculator are planning estimates; confirm quantities and prices with your supplier or contractor before you order.

Enter your project

in
cm

Finished floor to finished floor.

in
cm
in
cm

Results

Your results will appear here

Enter your measurements and press Calculate. Defaults show a typical example.

How to use the stair calculator

  1. Measure the total rise in inches between finished surfaces.
  2. Keep the maximum riser at your code limit (IRC: 7¾ in).
  3. Enter your tread depth (IRC minimum 10 in, measured nosing to nosing).
  4. Use the riser height and tread depth to mark the stringer with a framing square.

Formula

Risers = ⌈total rise ÷ max riser⌉; riser height = total rise ÷ risers; treads = risers − 1; total run = treads × tread depth; stringer ≈ √(rise² + run²).

Worked example

A 108 in rise: 108 ÷ 7.75 = 13.9 → 14 risers of 7.71 in, 13 treads at 10 in = 130 in of run, stringer about 169 in (14 ft 1 in).

Tips for using the stair calculator

  • Measure total rise from finished floor to finished floor, including flooring still to be installed.
  • Keep every riser within 3/8 in of the others; uneven steps cause trips.
  • Check local code for maximum riser height, minimum tread depth and handrail rules.
Elevated wood deck with railings overlooking a backyard in fall

Stair Calculator FAQs

How many steps for a 9 ft ceiling?

Total rise depends on floor thickness too, but around 108–118 in typically needs 14–16 risers at 7¾ in maximum.

Why is there one fewer tread than risers?

The top "tread" is the upper floor or landing itself.

What lumber do stringers use?

2×12s are common because the cut stringer must keep enough wood below the notches; check your code and plans.

Estimate before you call a contractor

Run the numbers with our free calculators so you can compare bids with confidence.

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