How Much Carpet Do I Need? Rolls, Seams and Underlay (UK)
Carpet is sold from a roll of a fixed width, so the amount you buy is a length from the roll. A room 4.5 × 3.2 m needs 3.30 m from a 5 m roll, which is 16.5 m² to pay for. The carpet calculator tries both roll widths and both directions and picks the smaller.
Carpet for common rooms
With 100 mm of trim, a plain carpet, and the better of a 4 m and a 5 m roll.
| Room | Roll | Length to buy | Seams | Area you pay for | Underlay rolls |
|---|---|---|---|---|---|
| 3 × 3 m | 4 m | 3.10 m | 0 | 12.4 m² | 1 |
| 3.5 × 3.5 m | 4 m | 3.60 m | 0 | 14.4 m² | 1 |
| 4 × 3 m | 5 m | 3.10 m | 0 | 15.5 m² | 1 |
| 4.5 × 3.2 m | 5 m | 3.30 m | 0 | 16.5 m² | 1 |
| 5 × 4 m | 5 m | 5.10 m | 0 | 25.5 m² | 2 |
| 5.5 × 4.5 m | 5 m | 5.60 m | 0 | 28.0 m² | 2 |
| 6 × 4.5 m | 5 m | 6.10 m | 0 | 30.5 m² | 2 |
How a pattern changes the length
For the room 4.5 × 3.2 m, each strip is longer by the length of the repeat so the pattern matches at a seam.
| Pattern repeat | Length to buy | Area you pay for |
|---|---|---|
| Plain | 3.30 m | 16.5 m² |
| 320 mm | 3.62 m | 18.1 m² |
| 640 mm | 3.94 m | 19.7 m² |
How the amount is worked out
- Strips. The number of strips is the width of the room plus the trim, divided by the width of the roll, rounded up.
- Length of a strip. The length of the room, the trim and any pattern repeat.
- Length to buy. The strips times the length of a strip. You pay for it at the full width of the roll.
- Direction. Running the strips the other way across the room sometimes saves a whole strip, so the calculator tries both.
Underlay and gripper
- Underlay comes in rolls of 11 m × 1.37 m, about 15 m². Order the floor area.
- Gripper goes round the walls, 6 to 8 mm from the skirting, and not across the doorways.
- Put a door bar at each doorway, to hold the edge of the carpet.
Before you buy
- Measure the longest length and width of the room, including alcoves and the doorway.
- Ask the shop to measure for stairs, a patterned carpet or an awkward room.
- Put any seam away from the door and the main light, and keep the pile running the same way.
See also the laminate flooring calculator and the skirting board calculator. These are estimates: a fitter will measure the room.
Frequently asked questions
How much carpet do I need?
Find how many strips of the roll cover the room, with 100 mm of trim on the length and the width. A room 4.5 × 3.2 m takes 3.30 m from a 5 m roll, which is 16.5 m² to pay for.
What width are carpet rolls in the UK?
Most carpet comes in 4 m rolls, and some ranges in 5 m. You pay for the whole width of the roll along the length you buy.
How much carpet should I add for waste?
The calculator adds 100 mm to the length and the width for trimming. A pattern needs one more repeat on every strip, and stairs, alcoves and bays need more.
How much underlay do I need?
The same area as the floor. A roll of 11 m × 1.37 m covers about 15 m², so 1 roll for 14.4 m².
Will the room need a seam?
Only if it is wider than one width of the roll after the trim: more than 3.9 m for a 4 m roll, or more than 4.9 m for a 5 m roll, in both directions.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.