Stair Carpet Calculator — Length, Area & Cost

Measure one tread depth (the flat part you step on, from nosing to riser), one riser height (the vertical face), and the stair width. Count the total number of treads. The carpet length per step is the tread depth plus the riser height plus an allowance for the nosing wrap and tucking/trimming. The standard UK carpet-trade rule of thumb is to add about 50mm (5cm) per step on top of tread + riser — roughly 25mm to wrap the nosing lip and 25mm to tuck and trim. So a 250mm tread with a 200mm riser needs about 500mm of carpet per step.

In the UK, stair carpet comes in two standard widths: 686mm (27 inches) for a runner with exposed stair edges, and 914mm for full-width coverage on a standard staircase. If your stairs are wider than 914mm, you may need standard broadloom carpet cut to width.

You need two gripper rod pieces per tread — one fitted into the angle where the tread meets the riser, and one at the back of the tread against the next riser. Gripper rods for stairs are typically cut to the stair width. Pre-cut stair gripper rods are available from carpet suppliers.

Yes, add 10% for fitting wastage and trimming. Stair carpet takes more skill to fit than flat floor carpet, and small errors in cutting can waste material. Some fitters also recommend buying an extra 300-450mm so you can shift the carpet up by one step in future to even out wear on the nosings.

The nosing overhang is the small lip where the front of the tread extends past the riser below — on most UK stairs around 20-30mm — which the carpet must wrap around. On top of that you also need a fitting/tuck allowance so the carpet can be tucked tight into the angle and trimmed cleanly. Our calculator defaults to 25mm nosing plus 25mm tuck, giving the standard 50mm (5cm) per-step allowance used across the UK carpet trade. Both figures are editable under Advanced Options if your stairs differ.