How to Measure Stairs for Carpet

Stairs trip people up because they are not an area to cover - they are a runner that wraps over the front of each step and down its face. So you do not measure a staircase in square feet; you measure the length of carpet it takes to follow the steps, and the width of the stair.

What to measure

1. Count the steps. Every tread that gets carpet is one step. Include a half-landing or winder treads.
2. Measure one step. Run the tape from the back of the tread, forward over the nosing (the lip at the front), and straight down the riser to the tread below. That length is the carpet per step. If you measure them separately, it is the tread (going) + the riser.
3. Measure the stair width. How wide the carpet has to be across the step - usually a bit under a metre for a domestic flight.

carpet per step = tread (going) + riser   (+ a little for the nosing wrap)
runner length   = steps × carpet per step

Worked example

A straight flight of 13 steps, 250 mm tread and 200 mm riser, 0.9 m wide:

1. Per step: 0.25 + 0.20 = 0.45 m.
2. Runner: 13 × 0.45 = 5.85 m.
3. Add wastage and the nosing wrap (about 10%): roughly 6.5 m of runner, 0.9 m wide.

Enter the steps, tread, riser and width as a staircase in the carpet calculator and it works the runner out and adds it to your rooms.

Watch out for

• Winders and landings. Curved winder treads need the carpet measured at the widest part of the tread, and a half-landing is an extra piece - measure it as its own small area.
• The nosing. Carpet wraps over the lip at the front of each tread, so add a little per step. The wastage allowance usually covers it, but on a long flight measure one step over the nosing to be sure.
• Pile direction. Carpet on stairs should run with the pile sweeping down the flight, so it wears and brushes the right way - this fixes which way the runner is cut and is why a stair runner is never seamed across the steps.
• Full width vs runner. A fully carpeted stair takes the whole stair width; a centred runner with painted edges takes less, but you still order by the runner length.

After the stairs

Add the landing and the rooms they connect to, and let the calculator pool the runs. Then size the underlay and the rest of the job - stair fitting is usually charged per step on top of the room rate, because it is slow, careful work.