About the Stair Calculator
Planning a staircase starts with the total rise, the vertical height from the lower floor to the upper floor. This stair calculator divides that height into equal risers as close as possible to the riser height you prefer, then gives the number of treads, the exact riser height, the total horizontal run, the diagonal stringer length and the angle of the stairs. It also checks the classic comfort rule that twice the riser plus the tread should be about 24 to 25 inches, and compares your layout with common code limits. It works in inches or millimetres.
Updated October 2026
How to use the Stair Calculator
- 1Choose inches or millimetres.
- 2Measure the total rise from the finished lower floor to the finished upper floor.
- 3Enter the riser height you would like, around 7 inches or 175 mm.
- 4Enter the tread depth you plan to use.
- 5Read the number of risers, the exact riser height, the total run and the stringer length.
Measuring the rise properly
Measure the total rise from the finished surface of the bottom floor to the finished surface of the top floor, not to the subfloor. If flooring will be added later, include its thickness. A mistake of even a few millimetres per step is noticeable underfoot, and uneven risers are a common cause of trips, which is why codes limit the difference between the tallest and shortest riser.
Quick design tips
- Keep every riser exactly the same height, which is why the tool recalculates it.
- A steeper stair saves floor space but is harder to climb and may break code.
- Add nosing of about 1 inch (25 mm) overhang if your design uses it, since this does not change the run in the tool.
- Allow at least 6 feet 8 inches (about 2 metres) of headroom above the stairs where your local code requires it.
Combine with other tools
Use the Pythagorean Theorem Calculator to check the stringer length, the Slope Calculator to see the gradient as a percentage, and the Unit Converter to move between inches, feet and millimetres. For materials, the Concrete Calculator covers poured steps, and the Area Calculator helps with finishes. This tool is a planning aid and is not a substitute for professional or code-compliant design.
Features
- Number of risers and treads
- Exact equal riser height, with a fraction of an inch
- Total run and stringer length
- Stair angle in degrees
- Comfort check using 2 x riser + tread
- Check against common riser and tread limits
- Inches or millimetres
Frequently asked questions
How do I calculate the number of steps for a staircase?
Divide the total rise by the riser height you would like and round to the nearest whole number. A rise of 108 inches divided by 7.5 is 14.4, so use 14 risers. The exact riser height is then 108 divided by 14, which is 7.71 inches, so all the steps are the same height.
Why are there fewer treads than risers?
The top riser ends at the upper floor, which acts as the last tread. A staircase with 14 risers therefore has 13 treads. The total run is the number of treads multiplied by the tread depth.
What is a comfortable riser and tread?
Most people find risers of 7 to 7.5 inches (175 to 190 mm) and treads of 10 to 11 inches (250 to 280 mm) comfortable. A common rule of thumb is that two risers plus one tread should equal about 24 to 25 inches, or roughly 610 to 635 mm.
What are the usual building code limits?
In many US residential codes the maximum riser is 7.75 inches and the minimum tread is 10 inches. Other countries and local codes differ, and may also set limits for headroom, handrails and winders. The tool gives a quick check against the common US limits, but always confirm with your local building authority.
What is a stringer and how long should it be?
A stringer is the sloping board that supports the treads. Its theoretical length is the diagonal of the right triangle formed by the total rise and total run. Buy a board a little longer than the figure shown, since the ends need to be cut and fitted.
Can I use this for deck steps or loft stairs?
Yes, as a layout guide for any straight flight. For decks, measure the height from the ground or landing to the deck surface. Winding stairs, landings and spiral stairs need extra planning that this tool does not cover.