How this calculator works
Worked example: a room 4.5 × 3.2 m is 14.4 m². With 100 mm of trim, a 4 m roll covers the 3.3 m width in one strip, and the strip is 4.6 m long, so you buy 4.60 m, which is 18.4 m² to pay for and 4.0 m² of offcut. A 5 m roll covers the 4.6 m length of the room across its width, in one strip of 3.30 m, so it is 16.5 m², and the best of the two is the 5 m roll. The underlay is 1 roll and the gripper 14.6 m with 0.8 m of doorway. A bigger room of 5.5 × 4.5 m needs 5.60 m from a 5 m roll. A pattern repeat of 640 mm adds to every strip: 3.94 m.
Carpet to buy for common rooms (best of 4 m and 5 m rolls, 100 mm trim, plain carpet)
The length from the roll and the area you pay for.
| Room | Roll | Length to buy | Seams | Area you pay for |
|---|---|---|---|---|
| 3 × 3 m | 4 m | 3.10 m | 0 | 12.4 m² |
| 3.5 × 3.5 m | 4 m | 3.60 m | 0 | 14.4 m² |
| 4 × 3 m | 5 m | 3.10 m | 0 | 15.5 m² |
| 4.5 × 3.2 m | 5 m | 3.30 m | 0 | 16.5 m² |
| 5 × 4 m | 5 m | 5.10 m | 0 | 25.5 m² |
| 5.5 × 4.5 m | 5 m | 5.60 m | 0 | 28.0 m² |
| 6 × 4.5 m | 5 m | 6.10 m | 0 | 30.5 m² |
Tips before you buy
- Measure the longest length and width of the room, including alcoves and the doorway, then let the calculator add the trim.
- A room up to 3.9 m across fits one width of a 4 m roll, and up to 4.9 m across one width of a 5 m roll, with the trim allowed for.
- Ask for the carpet to be cut in one piece where you can: a seam in a doorway or in a busy part of the room wears first.
- Put the underlay down in the opposite direction to the carpet, and tape the joints.
- For a patterned carpet, add one full repeat per strip, and ask the supplier how much they advise.
Tools & materials for this project
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Frequently asked questions
How much carpet do I need?
Find the strips that cover the room from a roll and add the trim: for a room 4.5 × 3.2 m, 3.30 m from a 5 m roll, which is 16.5 m² to pay for.
What width are carpet rolls?
Most UK carpets come in 4 m rolls, and some ranges in 5 m. You pay for the full width of the roll for the length you buy.
How much extra should I allow?
About 100 mm on the length and on the width for trimming, and one pattern repeat for a patterned carpet. Allow more for stairs, alcoves and bay windows.
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.
When do I need a seam?
When the room is wider than the roll after the trim: a room wider than 3.9 m on a 4 m roll, or wider than 4.9 m on a 5 m roll, in both directions.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.