Stair Calculator

Please enter all values greater than 0.
–risers (steps)
–actual riser height (in)
–treads
–total run (in)
–stringer length (in)
–stair angle

Check your local building code before building. Many codes limit risers to 7.75 in and require treads of at least 10 in.

How to use this calculator

Measure the total rise from the finished floor below to the finished floor above, in inches. Enter your preferred tread depth and a target riser height, then press Calculate. You get the number of steps, the exact riser height, the total run and the stringer length.

The formula

Risers = total rise ÷ target riser height (rounded)
Riser height = total rise ÷ number of risers
Treads = risers − 1
Total run = treads × tread depth
Stringer length = √(rise² + run²)

Example: A total rise of 108 inches gives 14 risers of about 7.71 inches, 13 treads, a total run of 130 inches and a stringer about 169 inches (14 ft 1 in) long.

Understanding your stair calculator results

The stair calculator turns one measurement, the total rise, into a full stair layout. The number of risers and the actual riser height matter most. Every step in a flight should be the same height, because people notice even small differences and are more likely to trip on them.

What changes the layout

  • Total rise. This is fixed by your floors. Measure it carefully, from finished floor to finished floor.
  • Target riser height. A lower target adds risers and makes the stair longer and easier to climb. A higher target saves space but feels steeper.
  • Tread depth. Deeper treads add to the total run and lower the stair angle.

A worked example

For a deck that sits 36 inches above the patio, a 7.5 inch target gives 36 ÷ 7.5 = 4.8, which rounds to 5 risers. Each riser is then 7.2 inches. That layout has 4 treads, so with 10 inch treads the total run is 40 inches. The stringer is the square root of 36 squared plus 40 squared, or about 53.8 inches. The stair angle comes out near 36 degrees, which is a comfortable slope.

Compare that with the 108 inch indoor rise in the formula section. It needs 14 risers and a 130 inch run, almost 11 feet of floor space. Check that you have this much room, plus a landing at the bottom, before you commit to a layout.

Practical tips and common mistakes

  • Measure the rise after flooring is installed, or add the flooring thickness to your number.
  • Buy stringer boards longer than the calculated length. The cut pattern and the top and bottom connections need extra.
  • Do not forget the thickness of the tread boards when you lay out the first riser. The bottom step is often cut short to make up for it.
  • Keep a few spare treads in mind for mistakes, especially with hardwood or composite.

Planning and cost

Most straight residential stairs use three stringers for a 36 inch width. Wider stairs usually need a stringer about every 16 inches. Treads, risers, handrails and balusters often cost more than the stringers, so price those out early. Stairs are a safety item. Confirm riser, tread, headroom and handrail rules with your local building department, and hire a licensed contractor if you are not sure.

Frequently asked questions

What is the maximum riser height?
Many building codes, including the US residential code, allow a riser of up to 7.75 inches. Always check your local code.
What is the minimum tread depth?
Most residential codes require a tread depth of at least 10 inches.
Why is the number of treads one less than the number of risers?
The upper floor acts as the last tread, so a staircase always has one more riser than treads.
How do I measure the total rise?
Measure vertically from the finished floor at the bottom to the finished floor at the top, including flooring thickness.
How many steps are needed for a 9 foot ceiling?
A floor-to-floor height of about 108 to 114 inches usually needs 14 or 15 risers.
How much headroom do stairs need?
Most US residential codes require about 6 feet 8 inches of headroom, measured straight up from the sloped line that connects the front edges of the treads. Low beams or a ceiling over the stair can block this. Check your plan early, because fixing headroom after framing is costly. Your local building department has the final word.
Do outdoor deck stairs follow the same rules as indoor stairs?
Usually yes. Most codes apply similar riser height, tread depth and handrail rules to deck stairs. Outdoor stairs also need a solid landing at the bottom, such as a concrete pad, and rot-resistant or treated lumber. Many areas require a permit for decks and their stairs, so check before you build.
When do stairs need a handrail?
Many residential codes call for a handrail once a stair has four or more risers. The rail is typically mounted 34 to 38 inches above the tread nosing and must be easy to grip. Open sides usually also need a guard. Rules vary by location, so confirm the details with your local code office.