Every riser must be equal
This is the rule that matters most and the one that is hardest to fix afterwards. People climb stairs by rhythm, not by looking. A single riser that differs from its neighbours by even ten millimetres is a genuine trip hazard, and it is the most common cause of falls on domestic stairs.
That is why the calculation starts from the total height and divides, rather than picking a step height and stacking them. Total floor-to-floor height divided by a whole number of risers gives equal steps by construction. The number you can choose is how many risers, not how tall each one is.
Measure floor-to-floor, not floor-to-ceiling, and measure finished floor levels. A 20 mm floor covering at the top and not the bottom throws every riser out.
The 2R + G rule
Stair comfort has a well-established relationship: twice the rise plus the going should fall between about 550 and 700 mm. The calculator reports this figure because it catches combinations that satisfy the individual limits but still feel wrong.
The reason is that rise and going trade off against each other. A tall riser with a deep tread makes you break stride; a shallow riser with a narrow tread makes you mince. The 2R+G figure captures the combination rather than each dimension alone.
Pitch is the other check. Domestic stairs are typically 32–38°, and most regulations cap private stairs somewhere around 42°. Above that you are into loft-ladder territory, which is governed by different rules.
| Measure | Comfortable range | Note |
|---|---|---|
| Rise per step | 175–200 mm | Must be identical on every step |
| Going (tread depth) | 225–300 mm | Deeper feels better on a shallow rise |
| 2 × rise + going | 550–700 mm | The combination check |
| Pitch | 32–38° | Most codes cap private stairs near 42° |
| Headroom | 2000 mm minimum | Measured vertically from the pitch line |
What the calculator cannot tell you
It gives the total run — the horizontal distance the flight occupies — and that is usually the constraint that forces a redesign. If the run does not fit the space, the options are a winder, a half landing, or a steeper flight, and each has regulatory implications.
Headroom is not calculated here and it catches people out on loft conversions constantly. You need clear vertical height above the pitch line for the whole flight, and a trimmer joist in the wrong place will fail that even when the rise and going are perfect.
Stairs are governed by building regulations in most jurisdictions, and the specifics differ on going, pitch, handrails, balustrade gaps and headroom. Treat this page as a design aid for working out whether an idea fits, and confirm the numbers against your local requirements before cutting timber.
When one stair becomes two flights
Most domestic stair guidance caps a single flight at sixteen risers before a landing is required. The number is not arbitrary — it is roughly where a fall stops being merely unpleasant — and a landing interrupts it.
So an ordinary storey of about 2.6 m is a single flight of thirteen or fourteen. A tall Victorian storey of 3.4 m or more comes out at eighteen risers, which has to be split, usually into two flights with a half-landing between them, often turning through 90° or 180° to fit the stairwell.
The landing has rules of its own: at least as deep as the stair is wide, and level throughout — a landing with a step in it is really two flights with a trap in the middle. The calculator now reports how many flights your total rise needs, so you know before framing anything whether the stairwell has to take a turn.
Common questions
How many steps for a given height?
Divide the floor-to-floor height by the maximum comfortable rise and round up. That whole number of risers then sets the exact rise per step.
What is the 2R+G rule?
Twice the rise plus the going should be between roughly 550 and 700 mm. It checks the combination rather than each dimension alone.
How much floor space will my stairs take?
The total run is the going multiplied by the number of treads, which is one fewer than the number of risers.