About the Stair Calculator
A stair calculator works out the number of risers, the exact riser height, and the stringer length from a total rise. Stair dimensions are heavily regulated because inconsistent steps are a leading cause of falls, and codes are specific about the tolerances.
The formula
Risers = round(total rise / target riser); Actual riser = total rise / risersTotal rise is the vertical distance between finished floor levels. Riser height is the vertical step, tread depth the horizontal walking surface. The number of treads is one fewer than the risers.
How to use this calculator
- 1Enter your Total Rise (vertical height, inches). The field starts at
108, which you can overwrite. - 2Enter your Riser Height (inches, 7–7.75 recommended). The field starts at
7, which you can overwrite. - 3Enter your Tread Depth (inches, 10–11 recommended). The field starts at
10, which you can overwrite. - 4Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| Total Rise (vertical height, inches) | 108 |
| Riser Height (inches, 7–7.75 recommended) | 7 |
| Tread Depth (inches, 10–11 recommended) | 10 |
Result
Number of Risers: 16
Actual Riser Height: 6.750 inches
Number of Treads: 15
Total Run: 150 inches (12.50 ft)
Stringer Length: 184.84 inches
Stair Angle: 35.8°
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
The number of risers must be a whole number, so the actual riser height is the total rise divided by that count — it rarely matches your target exactly. This is why you choose the riser count first and let the height fall out, rather than the reverse. Building codes require all risers within a flight to be within about 3/8 inch of each other, since the foot learns the rhythm of a staircase within two steps and an inconsistent one causes trips.
Comfort follows established rules of thumb. Riser plus tread should total 17 to 18 inches, and twice the riser plus the tread should fall between 24 and 25. The International Residential Code caps risers at 7¾ inches and requires treads of at least 10 inches, with headroom of 6 feet 8 inches minimum.
Things worth knowing
- All risers in a flight must be within 3/8 inch of one another. This is a code requirement, not a preference.
- Measure total rise between finished floor surfaces, accounting for flooring thickness at both levels.
- IRC limits: riser maximum 7¾ inches, tread minimum 10 inches, headroom minimum 6 feet 8 inches.
- There is always one fewer tread than riser in a flight.
- Check local code before building. Requirements vary between jurisdictions and commercial standards are stricter.
Frequently asked questions
What is the ideal riser height?+
7 to 7¾ inches is the comfortable range, with the International Residential Code capping residential risers at 7¾. Consistency within the flight matters more than the exact figure.
How do I calculate the number of stairs?+
Divide the total rise by your target riser height and round to a whole number, then divide the total rise by that count to get the actual riser height. It will rarely equal your target exactly.
What is the relationship between riser and tread?+
Two common rules: riser plus tread should total 17 to 18 inches, and twice the riser plus the tread should fall between 24 and 25. Both produce comfortable, natural-feeling stairs.
Why must all risers be the same height?+
Because people learn a staircase's rhythm within a couple of steps and then stop looking. An inconsistent riser breaks that expectation and causes falls, which is why codes limit variation to 3/8 inch.