Stair Carpet Calculator

Carpeting a flight of stairs

Here the flooring calculator starts in its stairs mode, with carpet chosen. Count the treads (not the landing or floor at the top: Online Carpets points out that the top riser is fitted with the landing’s carpet), then measure one step: the tread from front to back with the nose, the riser’s height, the stair’s width and how far the nosing sticks out past the riser. Old houses rarely have identical steps, so measure the deepest one.

Choose the style. For waterfall, each step needs its tread plus its riser. For Hollywood the carpet also tucks back under the nose, so the calculator adds the nosing once more. That Hollywood allowance is our estimate from the shape of the step, since no maker we checked publishes one; your fitter may want a little more. Every piece gets 5 cm for fitting and is cut 5 cm wider on each side, the allowances Online Carpets uses in its guide.

How the pieces come off the roll

Pile has to run down the stairs, and pile runs along the roll, so a step is never cut across the roll. Instead the pieces sit side by side: a 36 in stair cut 40 in wide gives three to a row on a 12 ft roll, and the drawing numbers every piece so you can see the rows and the hatched offcut beside them. A wider roll can save a whole row. Landings and winders are separate pieces measured at their widest and given 10 cm both ways; winders use the going at the outside edge, as Roger Oates measures them.

Runners and gripper

Tick the runner box for a runner with wood showing each side. Its length is the steps, the last riser and 50 cm a flight; compare styles and roll widths for 10 to 16 steps in the tables below. Gripper comes in 1.52 m lengths in the UK and tack strip in 4 ft pieces in the US (Roberts sells 48 in strips): one strip for every tread and, on a waterfall stair, one for every riser too. For stairs open on one side, CRI 105 turns the carpet under at the open edge and stops the gripper about 1½ in (38 mm) short.

Before you order

Cormar suggests allowing 10% extra on stairs because they are tricky to fit; the pieces here already carry their fitting allowance, so treat this as the least to buy and let your fitter confirm the cuts.

Carpet for a flight, by number of steps

Steps of 10 in treads and 7½ in risers with a 1 in nosing, 36 in wide: the roll length to buy with the pieces side by side, and a 27 in runner. Each piece carries 5 cm (2 in) for fitting and 5 cm each side.

The same in metric: 25 cm treads, 19 cm risers, 2 cm nosing, 85 cm wide, and a 70 cm runner.

Sources, checked September 2026: The Carpet and Rug Institute, CRI 105 residential installation standard (§15, carpet on stairs); Online Carpets, measuring stairs and landings (allowances, gripper, pieces on a 4 m roll); Cormar Carpets, planning and measuring and a guide to stair runners; Roger Oates, measuring guide (runner widths, length, winders); Godfrey Hirst, carpet installation (pile direction); Crucial Trading, stair carpet runners; Roberts, tack strip (48 in strips); 2018 International Residential Code §R311.7 and UK Approved Document K (step sizes the starting values fall within).