Carpet calculator
Carpet is sold off a roll, usually 4 m or 5 m wide, so you buy the roll width times the length you need. A 4 × 3.5 m room takes one 4.1 m piece from a 4 m roll: 16.4 m² of carpet for a 14 m² floor.
- Length off the roll
- 4.10 m
- Pieces
- 1
- Joins
- 0
- Room floor area
- 14.00 m²
- Offcut
- 14.6%
One piece 4.1 m long from a 4 m wide roll, with no joins.
For a plain carpet in a rectangular room. Patterned carpets, stairs and odd shapes need more: ask your fitter to measure before you order.
Carpet for common room sizes
Including 10 cm for trimming. The cheaper roll width for each room is the one with less to buy.
| Room | Floor area | From a 4 m roll | From a 5 m roll |
|---|---|---|---|
| 3 × 3 m | 9 m² | 12.4 m² | 15.5 m² |
| 3.5 × 3 m | 10.5 m² | 12.4 m² | 15.5 m² |
| 4 × 3.5 m | 14 m² | 16.4 m² | 18 m² |
| 4.5 × 4 m | 18 m² | 32.8 m², 1 join | 20.5 m² |
| 5 × 4 m | 20 m² | 32.8 m², 1 join | 25.5 m² |
| 5.5 × 4.5 m | 24.75 m² | 36.8 m², 1 join | 28 m² |
How we calculate this
We add the trimming allowance to the room’s length and width, then work out how to cut it from the roll with the least carpet. If one side of the room fits within the roll width, the room takes one piece. If not, you need more than one piece, joined together.
We try the carpet both ways round and pick the one that needs less. Carpet has a pile direction, so pieces in the same room should run the same way.
Questions people ask
Why do I need more carpet than my floor area?
Because you buy the full width of the roll. A room 3.5 m wide still uses 4 m of width from a 4 m roll, and the extra is cut off. Choosing the right roll width keeps the offcut small.
What width does carpet come in?
In the UK, mostly 4 m or 5 m. Some ranges only come in one width, so check before you plan your room.
How much underlay do I need?
About the floor area of the room, as underlay doesn’t need to match the carpet roll. Underlay is sold in rolls, so round up to whole rolls.
Should I measure in metres or centimetres?
Centimetres are safer. Write 368 cm rather than rounding to 3.7 m, so you don’t lose a few centimetres that could mean a join.
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