Standard Stair Rise and Run Calculator

What the calculator actually does

Rise and run are not independent numbers you pick freely - they are locked together by the total height of the flight (floor to floor) and by comfort and safety rules that have been refined over a century of stair building. A stair rise and run calculator divides your total rise by a target riser height to get a whole number of steps, then divides your total available run by one fewer tread (because the top step is usually the landing itself) to get the actual going per step. Change the total height by even 10mm and every riser in the flight shifts slightly, which is why site-built stairs are always calculated fresh rather than copied from a table.

This matters just as much for a stair runner calculator as it does for the joiner cutting stringers. A runner's total length is the sum of every tread's going plus every riser's rise, plus a wrap allowance at the top and bottom nosing. If your rise-and-run numbers are wrong by even half an inch per step on a 14-step flight, your ordered runner can come up short by 6-7 inches (15-18cm) - enough to leave the last tread bare.

US rules: IRC R311.7

• Maximum riser height: 7.75in (196.85mm) for most residential stairs under the IRC.
• Minimum tread depth (going): 10in (254mm), measured horizontally nosing to nosing.
• Riser variance across a flight: no more than 3/8in (9.5mm) difference between the largest and smallest riser.
• Minimum headroom: 6ft 8in (2032mm) measured vertically from the tread nosing.
• Handrail height: 34-38in (864-965mm) above the nosing line.

UK rules: Approved Document K / Part K

• Maximum rise: 220mm (8.66in) for private stairs; 190mm for stairs in common/public buildings.
• Minimum going: 220mm (8.66in) for private stairs.
• The 2R + G rule: twice the rise plus the going should fall between 550mm and 700mm for a comfortable pitch.
• Maximum pitch: 42 degrees for a private stair.
• Minimum headroom: 2m (6ft 6.75in) over the full width of the stair.

How to use rise and run to order a runner

1. Measure total floor-to-floor rise with a spirit level and tape, not by eye.
2. Divide by a target riser (7.5in / 190mm is a comfortable US/UK middle ground) to get a step count, then round to the nearest whole number.
3. Recalculate the exact riser height using that whole step count so every riser is identical.
4. Measure total horizontal run available and divide by (steps minus one) to get the going per tread.
5. Multiply (rise + going) by the number of steps, then add 24-36in (60-90cm) for top and bottom wrap, to size your runner order.
6. Cross-check the total against a stair runner length calculator before you buy, since hand arithmetic on a 15-step flight is where most ordering mistakes creep in.

Worked example

Take a flight with 2.6m (102.4in) of total floor-to-floor rise and 3.9m (153.5in) of horizontal run available. Dividing 2600mm by a target 185mm riser gives 14.05, which rounds to 14 steps. Recalculating: 2600mm / 14 = 185.7mm exact rise per step - comfortably under the 220mm UK maximum. For run, 14 steps means 13 treads (the 14th is the upper floor), so 3900mm / 13 = 300mm going, generous and well above the 220mm minimum. In US units that is roughly a 7.3in riser and an 11.8in going, both inside IRC limits with room to spare.

Rise and run change the runner order, not just the joinery

Steeper stairs (higher rise, shorter run) need more carpet per step because the riser face eats more fabric than the tread saves - which is counter-intuitive to most first-time buyers who assume a shorter tread means less material. A stair runner calculator accounts for this automatically by summing rise and run separately rather than using a flat per-step average, which is the shortcut that causes most DIY over- or under-ordering.

Common mistakes when calculating rise and run

When to bring in a professional

A calculator gets you the numbers, but a new stair build, a change in floor-to-floor height, or a flight with winders or a mid-landing genuinely needs a joiner or stair fitter to check the geometry against local code before anything is cut. For an existing flight where you are simply carpeting rather than rebuilding, the rise and run figures mostly serve one purpose: getting an accurate length for the runner order, which any competent DIYer can do with a tape measure and the formulas above.

Winders and stairs that are not a straight flight

A basic rise and run calculation assumes every step is a plain rectangle the same width as the stair, which is true on a straight flight but not on a stair with winders, a quarter-turn or a half-landing. Winders taper from a narrow point at the inside of the turn to a wide point at the outside, so the going varies across the width of a single tread rather than staying constant. Both the IRC and Approved Document K set a minimum going measured at a fixed point across a winder (typically 12in / 300mm in from the narrow edge), rather than an average, which means a rise and run calculator built for straight flights will understate the material needed at the turn if you simply carry the same per-step figure across winder treads.

For carpet ordering purposes this matters more than for the joinery, because a runner has to be cut and often seamed individually for each winder tread rather than following one repeating template. If your flight includes any winders, measure each winder tread separately at both its narrow and wide points before totalling the run, and treat that section of the order as bespoke rather than assuming the straight-flight formula covers it.

Rounding: metric to imperial and back again

Because US stairs are typically specified in inches and UK stairs in millimetres, a lot of small rounding errors creep in when a plan or product spec crosses between the two systems. A riser calculated as exactly 185mm becomes 7.28in, which most tape measures and most joiners will round to 7.25in or 7.3in - a difference of under a millimetre that is irrelevant to comfort but can matter if you are trying to hit a precise total flight height for a fixed floor-to-floor dimension.

In practice, always calculate in one unit system fully and convert only the final figures for communication, rather than converting at every intermediate step - repeated rounding across ten or fifteen steps is exactly how a flight ends up with a final riser that is visibly out of tolerance even though every individual conversion looked fine on its own.

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.