Stair Calculator
Work out risers, treads, riser height, total run, stair angle and stringer length, then check them against UK, US IRC or Canadian stair rules.
Reviewed by Dany, RightSums team · Updated
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home-energy · Daily life · UK & US
Enter the total rise from finished floor to finished floor, the tallest riser you want and the going (tread depth). The calculator rounds up to a whole number of equal risers, then gives the exact riser height, the number of treads, the total run, the stair angle, 2R+G and the stringer length along the pitch line. Add a stringer board width to see how much timber is left below the notches, and a headroom figure to test it. Then check the stair against Approved Document K for a private stair in England, the US International Residential Code R311.7, or the National Building Code of Canada 2020 Section 9.8. A 2,600 mm rise with 220 mm maximum risers needs 12 risers of 216.7 mm. Local building control has the final say.
Accepted inputs
- Total rise, floor to floor
- Tallest riser you want
- Going or tread depth
- Nosing projection
- Stringer board width (optional)
- Headroom (optional)
- Open risers and loft conversion
- Rule set: England, US IRC or Canada NBC
- Metric or imperial units
Outputs
- Number of risers and treads
- Exact riser height
- Total run
- Stair angle
- Stringer length
- 2R+G
- Notch depth and timber left on a cut stringer
- Pass or fail for each building rule, with its section number
How to use the Stair Calculator
- Enter the total rise between finished floors, the tallest riser you are happy with and the going of each tread, in millimetres or inches.
- The calculator divides the rise by your maximum riser, rounds up to a whole number of risers and shares the rise equally between them.
- It counts one tread fewer than risers, because the upper floor is the last step, then works out the total run, angle and stringer length.
- Pick England, the US IRC or Canada's NBC and each figure is checked against that document's limits, with the section number shown.
Frequently asked questions
How many stairs do I need for a 2.6 m floor to floor height?
You need 12 risers of 216.7 mm and 11 treads if your tallest allowed riser is 220 mm. Divide 2,600 by 220 and round up to 12. With a 250 mm going the flight runs 2,750 mm, sits at 40.9 degrees and has a 2R+G of 683 mm, all within Approved Document K for a private stair.
How many stairs do I need for a 9 foot rise?
A 108 in (9 ft) floor to floor rise needs 14 risers of about 7 11/16 in (195.9 mm) under the US limit of 7 3/4 in, plus 13 treads. With 10 in treads the run is 130 in (10 ft 10 in) and the stair angle is 37.6 degrees. Measure floor to floor, not floor to ceiling.
What are the UK building regulations for stairs?
For a private stair in England, Approved Document K Table 1.1 allows a rise of 150 to 220 mm and a going of 220 to 300 mm, with 2R+G between 550 and 700 mm and a pitch of no more than 42 degrees. Headroom should be 2 m, or 1.9 m at the centre of a loft conversion stair.
What is the maximum riser height for stairs in the US and Canada?
The 2021 International Residential Code (R311.7.5.1) caps risers at 7 3/4 in (196 mm), with treads of at least 10 in (R311.7.5.2) and 6 ft 8 in of headroom. Canada's National Building Code 2020 allows private stair risers of 125 to 200 mm and runs of 255 to 355 mm (Tables 9.8.4.1 and 9.8.4.2).
How long does a stair stringer need to be?
The stringer follows the pitch line, so its length is the square root of total rise squared plus total run squared. A 2,600 mm rise with a 2,750 mm run gives 3,785 mm (12 ft 5 in). A 108 in rise with a 130 in run gives 169.0 in (14 ft 1 in). Buy longer timber to allow for the end cuts.
Sources
The rates and rules in this tool come from:
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