Free construction calculator
Stair calculator
Enter the total rise and the riser height you want. You get the number of steps, the exact riser height, the run you need and the stringer length, checked against the IRC limits.
Result
| Risers (steps up) | 24 |
|---|---|
| Exact riser height | 7-1/2"7.5 in |
| Treads | 23One less than the risers: the top step is the floor |
| Total run | 19' 2"19.167 ft · 230 in |
| Stringer line length | 24' 4-1/16"Rise and run as a straight line, before the cuts |
| Stair angle | 36.9° |
| 2 risers + 1 tread | 25"Comfortable stairs land near 24" to 25" |
- Riser 7-1/2" is within the IRC maximum of 7¾".
- Tread 10" meets the IRC minimum of 10".
- The IRC allows at most 12' 7" (151") of rise in one flight. With 15' 0" you need a landing part way up.
- Run needed: 23 treads × 10" = 19' 2" of floor space, plus the landing at the bottom. Check your local code: it may differ from the IRC.
Ask Dex anything you’d calculate on site
Plain words, feet and inches. Dex shows the numbers and how it got them.
Dex does this and runs your whole business inside Northdesk → See Northdesk
How it works
Divide the total rise by the riser height you want and round to a whole number of risers. Then divide the total rise by that number to get the exact riser height: riser = total rise ÷ risers.
There is one tread fewer than risers, because the top step is the floor you arrive on: treads = risers − 1. The run is the treads times the tread depth: run = treads × tread depth.
The stringer line is the straight line from the bottom to the top: √(rise² + run²). Buy the stringer stock longer than this, for the cuts at the top and bottom.
The IRC (the model code most US towns adopt) allows risers up to 7¾", treads of at least 10", and at most 12' 7" of rise in one flight before a landing. Your town may differ; the inspector has the final word.
Worked example
15 ft of rise with 7½" risers. 15 ft is 180". 180 ÷ 7.5 = 24, so you build 24 risers at exactly 7½" and 23 treads.
The run. With 10" treads, the run is 23 × 10" = 230", or 19' 2" of floor space, plus a landing at the bottom. With 11" treads it grows to 253" (21' 1").
The catch. 180" is more than the 151" the IRC allows in one flight, so a 15 ft stair needs a landing part way up. The calculator flags that for you.
Questions people ask
How many steps do I need for a given height?
Divide the total rise in inches by your riser height and round. For 9' 4" (112") at about 7½", 112 ÷ 7.5 = 14.9, so 15 risers of 7.47" each and 14 treads.
What is the maximum riser height and minimum tread depth?
Under the IRC (residential): risers up to 7¾" and treads at least 10", with no more than ⅜" difference between the tallest and shortest riser in a flight. Commercial stairs under the IBC are stricter: 7" maximum and 11" minimum.
Why is there one less tread than risers?
The last riser lands on the upper floor, and that floor is the top "tread". So a stair with 15 risers has 14 treads cut into the stringer.
How long should the stringer board be?
At least the stringer line from the calculator, plus enough for the plumb cut at the top and the level cut at the bottom. For most stairs, buying the next size up (one or two feet longer) is right.
What is the 2R + T rule?
An old comfort rule: two risers plus one tread should land between about 24" and 25". A 7½" riser with a 10" tread gives 25", which is easy to climb.
Does the riser height include the finished floor?
Measure the total rise from finished floor to finished floor. If the flooring isn’t in yet, add its thickness, or the first and last steps will come out different from the rest.
More free calculators
- Square corner (3-4-5) calculatorThe diagonal that makes a corner 90°, and how far out a corner is.
- Concrete calculatorCubic yards and bags for slabs, footings and round columns.
- Paver and patio calculatorPavers, gravel base and bedding sand for a patio or walk.
- Roof pitch calculatorPitch, angle, rafter length and roofing squares.
- Block wall calculatorCMU block count, courses and mortar for a block wall.
- Gravel, mulch and topsoil calculatorCubic yards, tons and bags for any area and depth.
- Slope and grade calculatorDrop over a run, inches per foot, percent grade and degrees.
Built by Northdesk
These calculators are made by Northdesk, construction business software with Dex, an AI assistant, built in.
- General contractorsSubs to bid, insurance certificates to chase, inspectors to meet, owners to keep happy and a budget to protect.
- Masonry contractorsBlock, brick, stone and mortar on the right site, the saw and the mixer where they should be, and a crew that speaks two languages on the same page.
- Project managementOne page per project with today’s work up front, and the whole business around it: crew, schedule, subs, materials and money, in one place, with Dex built in.
Run the day from one desk.
We’ll set Northdesk up around your company: your name, your logo, only what you use. Dex will book you a walkthrough with our team.