Stair guide
Stair rise and run: how to calculate your stairs
Every comfortable staircase comes from the same few numbers: the total rise (floor-to-floor height), the number of risers, the height of each riser and the depth of each tread. Get these right and the rest of the design follows.
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Open the stair calculatorEnter your total rise and run, compare riser counts and see the stair drawn as you adjust it.
Stair terms in one minute
- Total rise: the vertical distance from the finished lower floor to the finished upper floor.
- Riser (rise): the height of one step.
- Tread or going: the horizontal depth of one step.
- Total run: the horizontal distance the whole flight covers.
- Pitch: the angle of the stair, measured from horizontal.
How to calculate the number of steps
- Measure the total rise from finished floor to finished floor.
- Divide by the maximum riser height allowed where you live, and round up to get the number of risers.
- Divide the total rise by that number of risers to get the exact height of every riser. All risers in a flight should be equal.
- Choose a tread depth. A flight has one fewer tread than risers, because the upper floor acts as the last tread.
- Multiply the number of treads by the tread depth to get the total run.
Worked example (metric)
Total rise 2,700 mm. Choose 14 risers: 2,700 ÷ 14 = 192.9 mm per riser. With a 250 mm tread there are 13 treads, so the total run is 13 × 250 = 3,250 mm. The pitch is about 37.6 degrees, and twice the riser plus the tread is 636 mm, which sits in the comfortable range used by UK and South African guidance.
Worked example (imperial)
Total rise 108 in (9 ft). Dividing by the 7¾ in US residential maximum gives 13.9, so use 14 risers: 108 ÷ 14 = 7.71 in each. With a 10 in tread there are 13 treads, so the run is 130 in (10 ft 10 in). The pitch is again about 37.6 degrees.
Typical limits by region
| Region | Riser and tread | Other commonly quoted limits |
|---|---|---|
| United States (IRC R311.7) | Riser up to 7¾ in (196 mm). Tread at least 10 in (254 mm). | Riser and tread variation within a flight no more than ⅜ in. Headroom at least 6 ft 8 in. |
| United Kingdom (Approved Document K, private stairs) | Rise up to 220 mm. Going at least 220 mm. | Pitch no more than 42°. Twice the rise plus the going between 550 and 700 mm. Headroom at least 2 m. |
| South Africa (SANS 10400-M) | Limits depend on the stair type and edition. Check the standard. | Going plus twice the riser is commonly given as 570 to 650 mm. Headroom of at least 2.1 m is required over the stair. |
The 2R + G comfort rule
Twice the riser plus the going (2R + G) is a quick check that a stair will feel natural to climb. The UK guidance range is 550 to 700 mm and the South African figure is tighter at 570 to 650 mm. If your numbers fall outside the range, change the riser count or the tread depth and recalculate.
Common stair mistakes
- Measuring to the structural floor instead of the finished floor, which makes the first or last riser different from the rest.
- Mixing riser heights. Even small differences are a trip hazard and a common inspection failure.
- Forgetting headroom, especially where the stair passes under a beam or the next floor.
- Designing the stair first and only then checking the available run.
Frequently asked questions
How do I calculate stair rise and run?
Divide the total rise by your maximum riser height and round up to get the number of risers, then divide the total rise by that number for the exact riser height. Multiply the number of treads (one fewer than risers) by the tread depth to get the total run.
What is the maximum riser height for stairs?
For US residential stairs the IRC maximum is 7¾ inches (196 mm). UK private stairs allow up to 220 mm. Check the rules where you live.
How many treads are there compared with risers?
A straight flight has one fewer tread than risers, because the upper floor takes the place of the last tread.
What is the 2R + G rule?
Twice the riser height plus the tread depth should fall within a comfortable range, commonly 550 to 700 mm in UK guidance. It is a quick check that a stair will not feel too steep or too shallow.
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