Home & Construction⏱ 4 min read
How to Calculate Carpet for Stairs: A Step-by-Step Guide
Stair carpeting wastes a surprising amount of material if measured incorrectly. Here is the precise method, the difference between waterfall and wrap installation, and how to order.
Stair carpet is sold by the linear metre (for a set width) or by the square metre. The calculation seems simple but trips up most DIYers — the two installation methods have very different material requirements.
Measuring a Single Step
Each step consists of:
Tread: horizontal surface (typically 240-280mm deep)
Riser: vertical face (typically 170-220mm high)
For carpet that covers tread AND riser:
Length per step = Tread depth + Riser height
Example: 250mm tread + 190mm riser = 440mm per step
For 13 stairs:
Total length = 13 x 440mm = 5,720mm = 5.72m
Standard stair carpet width:
Available in 67cm, 1m (full width), or 4m broadloom
Most UK stairs: 900-920mm wide
Order: 1m wide carpet at 5.72 linear metres
Waterfall vs Wrap Installation
Waterfall (most common for patterned carpet):
Carpet falls straight down from tread edge to floor
Does NOT follow the step profile closely
Material per step = Tread depth + Riser height
(same as above measurement)
Wrap installation (neater finish, uses more carpet):
Carpet folds under and tucks into step nosing
Extra 50-75mm per step for the fold
Material per step (wrap): Tread + Riser + 60mm tuck
For 13 stairs at 490mm per step: 6.37m linear
Pad/underlay:
Only on the tread (not riser) in most installations
13 treads x 250mm = 3.25m at stair width
Landing and Half-Landing
Landing area measured as a rectangle:
Landing: 900mm wide x 900mm deep = 0.81 m2
Add to stair calculation:
13 stairs of 1m wide carpet at 5.72m: 5.72 m2
Landing 0.9m x 0.9m: 0.81 m2
Total: 6.53 m2
Add 10% waste: 6.53 x 1.10 = 7.18 m2 → order 7.5 m2
Pattern repeat considerations:
Patterned carpet needs extra for repeat matching.
Add one full pattern repeat per stair (typically 50-100mm extra)
For 13 stairs with 75mm repeat: add 975mm ≈ 1m extra to order