Home & Construction📅 8 April 2025⏱ 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.
JW
James WhitfieldPersonal Finance & Maths WriterJames has written about personal finance, health metrics, and everyday mathematics for over six years. He holds a BSc in Mathematics from the University of Leeds.
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