Stair Measurements Calculator: Every Dimension You Need Before You Build

The measurements that define a staircase

Every other stair dimension is derived from two starting numbers: total rise, the vertical distance between the two finished floor levels the stair connects, and total run, the horizontal distance available for the stair to occupy. From those two figures, and a target riser height, you can calculate riser count, exact riser height, tread run (also called the going in UK terminology), total run, stringer length, headroom clearance, and pitch (the overall angle of the stair). Getting total rise measured accurately matters more than any other single figure, because every riser height calculation depends on it - measure from finished floor surface to finished floor surface, including the thickness of any flooring, tile or runner that will be added later, not from subfloor to subfloor.

The distinction between rise, run and going trips up a lot of first-time stair planners, particularly across the Atlantic where terminology differs slightly. In US usage, 'run' commonly refers to both the total horizontal distance of the whole flight and the depth of a single tread; in UK usage, 'going' specifically means the depth of a single tread (the horizontal distance from one nosing to the next), while 'going' of the whole flight is the total horizontal run. This guide uses 'tread run' for the single-step measurement and 'total run' for the whole flight to avoid ambiguity.

Core formulas

The 7-11 rule and comfort formula

The 7-11 rule - a 7 in (17.8 cm) riser paired with an 11 in (28 cm) tread run - is the most commonly cited starting point for comfortable residential stairs, and it isn't arbitrary: it satisfies the older comfort formula of 2 x riser + 1 x run landing between about 24-25 in (61-63.5 cm), a relationship long used across stair-building trades to check that a stair isn't unconsciously too steep or too shallow for a natural stride. A second common comfort check is riser + tread run summing to roughly 17-18 in (43-46 cm), which serves as a quick sanity check alongside the 2R+T formula rather than replacing it. Neither formula is a legal limit by itself - they're design guidance that sits inside whatever your local code's hard maximums and minimums allow.

Code limits: IRC and UK Part K

In the US, the IRC generally caps riser height at 7.75 in (196 mm) and sets a minimum tread run of 10 in (254 mm) for residential stairs, with riser variance across a single flight held to a tight tolerance, commonly cited around 3/8 in (10 mm). In the UK, Building Regulations Approved Document K caps riser height at 220 mm (8.7 in) for a private stair, with a minimum going of 220 mm as well, and limits overall pitch to 42 degrees for a private stair. Both codes also set minimum headroom - commonly 6 ft 8 in (2.03 m) in US residential guidance, and 2 m (6 ft 6.75 in) in UK guidance, measured as the clear vertical distance above the nosing line of the stair, not straight up from the floor below.

Worked full example

Take a stair connecting two floors with a total rise of 108 in (2.74 m) and 120 in (3.05 m) of available total run. Target a 7.2 in (18.3 cm) riser: 108 ÷ 7.2 = 15 risers exactly, so no rounding needed here, and 15 risers give 14 treads. At an 11 in (28 cm) tread run, 14 treads need 154 in (3.91 m) of total run, which exceeds the 120 in (3.05 m) available - so either the tread run has to shrink toward the 10 in (25.4 cm) IRC minimum, or a winder/turn needs to be introduced to fit the stair into the available footprint. Shrinking tread run to 10 in gives 14 x 10 = 140 in (3.56 m), still over the 120 in available, which tells you plainly that a straight single flight doesn't fit this footprint and a turn, winder, or a steeper (but still code-legal) riser/run combination is genuinely required - a good example of why total run has to be checked early, not assumed to work out.

Measurement sequence

1. Measure total rise, finished floor to finished floor, including any flooring or runner thickness planned.
2. Measure total run available in the space, checking for any obstruction like a doorway or wall.
3. Divide total rise by a target riser height and round to a whole riser count.
4. Divide total rise by that riser count for the exact, equal riser height.
5. Multiply tread run by (riser count minus one) to get total run required, and compare to space available.
6. Check pitch (arctan of rise over run) and headroom against your code's limits before finalising.

How much runner do I need?

Once rise, run and riser count are confirmed, runner length follows directly. For a 13-step flight at a 10 in (25 cm) tread run and 7.5 in (19 cm) riser, each step consumes roughly 17.5 in (44.5 cm) of runner across tread, riser and nosing, totalling about 19 ft (5.8 m) for the flight before allowances. In metric, that's a 25 cm going and 19 cm riser, using 44.5 cm per step, or roughly 5.8 m for 13 steps. Add a 5-10% waste allowance for pattern matching and trims, bringing the practical order to about 20-21 ft (6.1-6.4 m). A stair runner calculator applies this exact arithmetic to your own confirmed measurements, and a stair runner length calculator will also flag if your riser count doesn't match a whole number of pattern repeats.

Measuring headroom correctly

Headroom is measured perpendicular to the pitch line of the stair (an imaginary line touching the front edge, or nosing, of every tread) up to the underside of any structure above - a ceiling, a floor joist, or the underside of a stair above it in a stacked staircase configuration - not as a simple vertical measurement from the tread surface. This distinction matters most at the point where headroom is tightest, usually partway up the flight where the stair above (in a stacked configuration) or a low ceiling beam is closest to the pitch line. Measure at several points along the flight, not just top and bottom, since the minimum headroom point is often mid-flight rather than at either end.

Whatever you decide, get the numbers first: the stair runner calculator doubles as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length the first time.

Still deciding on material, width or pattern? Our hub on stair runners compares weaves, widths, backings and fitting styles side by side, then hands the numbers straight to the calculator.