Waist to Height Ratio
The measure BMI structurally cannot give you.
Health & Home
Stair Calculator
Rise, going and headroom against building limits.
What it does. Divide floor-to-floor height by a target riser height, round to a whole number of risers, then divide back to get the exact rise. Every riser in a flight must be equal — an uneven one is the single most common cause of a fall on stairs.
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How to use Stair Calculator
- Enter the total floor-to-floor height.
- Set a target riser height and the going.
- Check the result against the regulation limits shown.
Every riser must be identical
People climb stairs by pattern, not by looking. After two or three steps the foot goes where the previous risers put it, so a step that differs by even 10mm catches the toe.
This is why regulations require equal risers throughout a flight, and why the calculation always starts from a whole number of risers.
The classic failure is the last step. Someone builds a flight to a nominal riser height, and whatever is left over becomes a different final step at the top — precisely where a trip is most dangerous.
Regulation limits
| UK domestic | US (IRC) | |
|---|---|---|
| Max riser | 220mm | 7¾in (196mm) |
| Min going / tread | 220mm | 10in (254mm) |
| Max pitch | 42° | — |
| Min headroom | 2000mm | 6ft 8in (2032mm) |
| Max variation in a flight | — | ⅜in (9.5mm) |
| Min width | — | 36in (914mm) |
The US limits produce a noticeably shallower, more generous stair than the UK ones. These are also the minimums for compliance, not targets for comfort — a stair built exactly to the UK maximum pitch is legal and steep.
Rules of thumb worth knowing
Two rises plus one going should total roughly 550 to 700mm. It encodes the natural relationship between step height and stride, and a stair that satisfies it feels right underfoot.
Riser plus going of around 430 to 450mm is another common check.
These are guides, not regulations, and they can conflict with fitting a stair into a tight space. Where they do, the regulations decide — but a stair that fails both rules of thumb while passing the regulations will feel awkward every day for its whole life.
Frequently asked questions
How do I calculate the number of stairs?
Divide the total floor-to-floor height by your target riser height and round to a whole number. Then divide the height back by that number for the exact rise — which is what makes every riser equal.
What is the maximum step height?
220mm for UK domestic stairs; the US IRC allows 7¾ inches, about 196mm. Both are compliance limits rather than comfortable targets.
Why must every step be the same height?
People climb by pattern rather than by looking, so a step differing by even 10mm catches the toe. The last step at the top is the classic failure and the most dangerous place for it.
What is the 2R plus G rule?
Two rises plus one going should total roughly 550 to 700mm. It encodes the relationship between step height and natural stride, and stairs satisfying it feel right underfoot.
How much headroom do stairs need?
2000mm in the UK and 6 feet 8 inches (2032mm) under the US IRC, measured vertically from the pitch line of the stair.