Loading calculator...
- Number of risers = total rise ÷ target riser height, rounded to a whole number.
- Riser height = total rise ÷ number of risers. There is one fewer tread than risers.
- A 42 inch rise needs 6 risers of 7 inches and 5 treads of 10.5 inches.
- Many building codes limit risers to about 7¾ inches and require treads of at least 10 inches.
How to use the stair calculator
Measure the total rise
Measure the vertical distance from the bottom floor or ground to the top landing, in inches.
Set the riser and tread
Enter the riser height you would like and the tread depth. 7 to 7½ inches and 10 to 11 inches are common starting points.
Add the width
In the advanced options, enter the stair width to see how many stringers you need at 16 inch spacing.
Read the result
You get the number of risers and treads, the exact riser height, total run, stringer length and the stair angle.
How stairs are calculated
Every step in a staircase must be the same height, so the total rise is divided evenly. First find how many risers fit, then divide the total rise by that number. The run is the number of treads times the tread depth, and the stringer is the sloped board that runs along the diagonal.
Stair formulas
Risers = total rise ÷ target riser, rounded
Riser height = total rise ÷ number of risers
Treads = risers − 1
Total run = treads × tread depth
Stringer length = √(total rise² + total run²)
Angle = arctangent of (total rise ÷ total run)
A common comfort check is 2 × riser + tread between about 24 and 25 inches.
Worked examples
A 42 inch rise
Target riser 7.25 inches and tread 10.5 inches. 42 ÷ 7.25 = 5.8, which rounds to 6 risers.
2 × 7 + 10.5 = 24.5 inches, within the comfort range.
A 30 inch deck
Target riser 7.5 inches and tread 10 inches.
Short decks need only a few steps.
A 100 inch rise
Target riser 7 inches and tread 10.5 inches. 100 ÷ 7 = 14.3, which rounds to 14 risers.
Check that you have space for the run.
Common stair limits
Typical residential figures
Many codes use limits like these. Yours may differ.
Always confirm the rules with your local building department.
Where a stair calculator helps
Deck stairs
Plan the steps from a deck to the ground.
Basement and attic stairs
Check the run you need for a given height.
Porches and entries
Plan a few steps up to a door.
Cutting stringers
Get the length, angle and number of stringers before you buy lumber.
Stair rules for riser height, tread depth, headroom, handrails and guards depend on where you live and on the type of building. This calculator gives a starting layout and is not a substitute for the building code or an inspection. For structural work, ask a qualified builder.
Stair calculator FAQ
How do I calculate the number of steps?
Divide the total rise by the riser height you want and round to the nearest whole number. A 42 inch rise at about 7¼ inches per riser gives 6 risers.
How many treads are there?
One fewer than the number of risers, because the top landing acts as the last tread.
What is a good riser height and tread depth?
Many people use risers of 7 to 7½ inches and treads of 10 to 11 inches. Many codes limit risers to about 7¾ inches and require treads of at least 10 inches.
What is total run?
It is the horizontal distance the stairs cover, found by multiplying the number of treads by the tread depth.
How long is the stringer?
Use the Pythagorean theorem with the total rise and total run. For a 42 inch rise and 52½ inch run, the stringer is about 67¼ inches.
How many stringers do I need?
This calculator suggests enough to keep spacing at or under 16 inches across the width of the stairs. Your tread material may allow different spacing.