Stair Calculator - calculatorsee.com


Stair Calculator

Calculate staircase dimensions, number of risers, tread depth, stringer length, and incline angle matching International Building Code (IBC).

Calculator Inputs

in
Finished lower floor to finished upper floor (105" = 8 ft 9 in).
in
Code maximum is 7.75 inches.
in
Code minimum is 10.0 inches.

Calculated Results

Staircase Layout
14 Risers @ 7.50" each
Number of Treads 13 Treads (10.50" depth)
Total Staircase Run 136.50 inches (11 ft 4.5 in)
Stringer Length 172.22 inches (14 ft 4.2 in)
Incline Angle 35.54° (Optimal 30°-37°)
Values calculate live as you adjust inputs.

About Stair Calculator

Computes staircase geometry matching residential building codes: calculates exact riser heights, number of treads, stringer length, and incline pitch.

What is Stair Calculator?

Computes staircase geometry matching residential building codes: calculates exact riser heights, number of treads, stringer length, and incline pitch.

How to Use This Calculator

  1. Measure total vertical rise from finished lower floor to finished upper floor.
  2. Adjust target riser and tread depth.
  3. Review exact riser count, total horizontal run, and stringer length.

The Mathematical Formula & Variables

Risers = round(Total Rise / Target Riser); Exact Riser = Total Rise / Risers; Treads = Risers - 1; Total Run = Treads * Tread Depth; Stringer = sqrt(Rise^2 + Run^2)

Step-by-Step Worked Example

Scenario: Total rise of 105 inches with 7.5 inch target risers and 10.5 inch treads.

  1. 105 / 7.5 = 14 risers exactly.
  2. Each riser = 105 / 14 = 7.50 inches.
  3. Treads = 14 - 1 = 13 treads.
  4. Total run = 13 * 10.5 = 136.50 inches.
  5. Stringer = sqrt(105^2 + 136.5^2) = 172.22 inches (14 ft 4 in).
  6. Incline angle = arctan(105 / 136.5) = 35.54°.

Result: 14 Risers @ 7.50" | Run: 136.5"

Frequently Asked Questions

What is the Blondel rule for comfortable stairs?

The historic architectural rule states that 2 * Riser + Tread should equal 24 to 25 inches (e.g. 2*7.5 + 10 = 25).