Stair Calculator – Rise, Run & Angle
Free stair calculator to determine the number of steps, riser height, going, and stair angle. Enter total rise and run for instant results.
Stair Calculator Formula
Steps = Total Rise ÷ Ideal Riser Height; Angle = arctan(Rise / Run)
How to Calculate Stair
- 1. Determine number of steps: Steps = round(Total Rise ÷ 7.5)
- 2. Calculate actual riser height: Riser = Total Rise ÷ Steps
- 3. Calculate going per step: Going = Total Run ÷ Steps (or use default tread depth)
- 4. Calculate stair angle: Angle = arctan(Total Rise ÷ Total Run) × (180 / π)
- 5. Ideal riser height is between 7 and 7.5 inches per building codes
Example Calculation
Let's say you're building a staircase with a total rise of 108 inches and a total run of 120 inches.
- totalRise: 108
- totalRun: 120
- treadDepth: 10
14 steps with 7.71 in risers, 10 in going, and a 42.0° stair angle
Tips
- Ideal riser height is 7–7.5 inches. Most building codes require risers between 4–7.75 inches
- Tread depth should be at least 10 inches per IRC and IBC standards
- All risers in a flight must be within 3/8 inch of each other for uniformity
- The rule of thumb: 2×Riser + 1×Going should equal 24–25 inches for comfortable stairs
- Add 5% extra material for waste when ordering treads and risers
Frequently Asked Questions
What is the ideal riser height for stairs?
The ideal riser height is between 7 and 7.5 inches. This provides a comfortable stride for most people. Residential codes typically allow 4–7.75 inches, but 7–7.5 is the sweet spot.
How do you calculate the angle of stairs?
The stair angle is calculated using arctan(total rise ÷ total run) converted to degrees. A comfortable residential stair angle is between 30° and 37°.
How many steps do I need for a 9-foot ceiling?
For a 9-foot ceiling (108 inches total rise), you need approximately 14–15 steps at 7.2–7.7 inches per riser.
What is the 2R+G rule for stairs?
The 2R+G rule states that twice the riser height plus the going (tread depth) should equal 24–25 inches. For example, 2×7 + 11 = 25 inches, which is a comfortable stair proportion.