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Stair Calculator: Rise, Run, Risers and Treads
Enter your total rise and we’ll do the math: how many steps you need, the exact riser height, the total run and the stair angle, all checked against building code.
Measure straight up from the finished floor at the bottom to the finished floor at the top.
ftin
Riser face to riser face. Code minimum is 10″. 10″ to 11″ is typical.
in
Fill this in only if your total run is fixed. We’ll size the treads to fit.
ftin
Based on the International Residential Code (IRC). Local codes vary, so check with your building department.
How to Measure Your Total Rise
- Measure straight up from the finished floor at the bottom of the stair to the finished floor at the top.
- Use the finished height of both floors. If you’re adding hardwood, tile or carpet later, add its thickness now.
- Measure in two or three spots. Floors aren’t always level, so use the average or the spot where the stair will sit.
How the Math Works
1. Count the risers. Divide the total rise by 7-3/4″ (the code maximum) and round up. A 105″ rise divided by 7-3/4″ is 13.5, so you need 14 risers.
2. Find the riser height. Divide the total rise by the number of risers. 105″ divided by 14 is 7-1/2″ per riser.
3. Count the treads. You need one less tread than risers, because the top floor acts as the last step. 14 risers means 13 treads.
4. Find the total run. Multiply the number of treads by the tread run. 13 treads at 10″ is 130″ (10′ 10″) of floor space.
5. Check the comfort. Two risers plus one run should land between 24″ and 25″. 7-1/2″ + 7-1/2″ + 10″ = 25″, right in the sweet spot.
Stair Building Code Basics
Most U.S. homes follow the International Residential Code (IRC). Here are the numbers that matter most:
| Rule | IRC requirement |
|---|---|
| Riser height | 7-3/4″ maximum |
| Tread run | 10″ minimum, riser face to riser face |
| Nosing | 3/4″ to 1-1/4″ when the run is under 11″ |
| Riser and tread variation | No more than 3/8″ between the tallest and shortest riser (or deepest and shallowest tread) |
| Headroom | 6′ 8″ minimum, measured straight up from the nosing line |
| Stair width | 36″ minimum |
| Handrail height | 34″ to 38″, measured straight up from the nosing |
Local codes can be stricter, and commercial buildings follow different rules. Always check with your local building department before you build.
Replacing Treads on an Existing Stair
If you’re remodeling, your rise and run are already set. The thing to watch is the first and last riser.
- If new treads sit higher than the old ones (for example, retrofit treads installed over the old treads), every middle step rises the same amount, so those risers stay equal. The bottom riser gets taller and the top riser gets shorter by that amount.
- New flooring at the bottom or top changes those risers too. Thicker flooring at the bottom makes the first riser shorter.
- Measure your top and bottom risers before you order. Code allows only 3/8″ of difference between risers.
See our retrofit stair tread kits and stair treads and risers.
Stair Calculator FAQ
How do I calculate stair rise and run?
Divide your total rise by 7-3/4″ and round up to get the number of risers. Divide the total rise by that number to get each riser height. Treads are one less than risers. Multiply the treads by your tread run (10″ or more) to get the total run.
How many steps do I need?
It depends on your exact floor-to-floor height, so measure it. A 105″ rise needs 14 risers at 7-1/2″. A 117″ rise needs 16 risers at 7-5/16″.
What is the maximum stair riser height?
The IRC allows up to 7-3/4″ for homes. Many builders aim for 7″ to 7-1/2″ because it’s easier to climb.
What is the minimum tread depth?
The IRC requires at least a 10″ run, measured from riser face to riser face. Add your nosing to get the full tread depth. A 10″ run with a 1-1/4″ nosing needs an 11-1/4″ deep tread.
What is the most comfortable stair rise and run?
Two risers plus one run should equal 24″ to 25″. A 7-1/2″ riser with a 10″ run (25″) or a 7″ riser with an 11″ run (25″) both feel natural.
Do I count the top floor as a step?
The top floor counts as the last step, but you don’t buy a tread for it. That’s why you always need one less tread than risers.