How To Calculate Carpet Roll Requirements
Quick answer
Divide the room width by the roll width and round up: that is the number of drops. Each drop is the room length plus about 10 cm trim. Multiply drops by cut length for the linear metres off the roll, then by the roll width for the square metres you pay for. Work it out both ways round and with each roll width, and take the cheapest that keeps joins out of the way.
Definition
Carpet roll requirements are the length of carpet you need to cut from a roll of fixed width (usually 4 m or 5 m) to cover a room, including trim and any extra widths joined in.
Explanation
You do not buy carpet by the room’s area. You buy a length off a roll of fixed width, so a room that is just wider than the roll needs a whole second drop. That is why roll width and the direction you lay it matter more than the room’s square metres. Always plan from the room’s full rectangle, even where alcoves or chimney breasts cut into it, because the carpet still comes off the roll as a rectangle.
5.2 m × 4.3 m room (22.4 m²): what you actually order
| Roll and direction | Drops | Order | Joins |
|---|---|---|---|
| 4 m roll, along the 5.2 m length | 2 × 5.30 m | 42.4 m² | 1 |
| 4 m roll, along the 4.3 m width | 2 × 4.40 m | 35.2 m² | 1 |
| 5 m roll, along the length | 1 × 5.30 m | 26.5 m² | None |
Examples
- 3.4 m × 3.1 m bedroom on a 4 m roll: one drop of 3.20 m = 12.8 m², no join.
- 4.6 m × 3.8 m lounge on a 4 m roll: one drop of 4.70 m = 18.8 m², no join.
- 5.2 m × 4.3 m lounge: 35.2 m² on a 4 m roll with a join, or 26.5 m² on a 5 m roll with none.
Summary
Plan drops, not square metres. Use the free carpet roll calculator for single rooms, or the PlanCutFit floor planner to plan every room and the stairs on the same roll.
In depth
Step by step
1. Measure the room’s full rectangle
Measure the longest length and widest width, into bays and alcoves. Write down which wall the door and main window are on, as they decide where joins can go and which way the pile should run.
2. Count the drops each way round
Drops = room width ÷ roll width, rounded up. Then swap length and width and do it again. A room 4.3 m wide needs two drops on a 4 m roll but one on a 5 m roll.
3. Add trim and work out the length
Cut length = the side the drops run along + trim (10 cm is a common total). Linear metres = drops × cut length. Square metres to order = linear metres × roll width.
4. Check the joins and pile
Keep joins out of doorways and walkways, and run the pile the same way in rooms that meet. If fixing the pile costs extra carpet, put it on the quote rather than absorbing it.
- Joins away from doorways
- Pile towards the main light
- Same pile direction through connected rooms
5. Use the offcuts
A strip left beside the last drop is often enough for a cupboard, a landing or a few steps. Plan the whole job together and you can cut stairs from the waste of the rooms.
Frequently asked questions
- How do I convert linear metres of carpet to square metres?
- Multiply the linear metres by the roll width. 6 linear metres off a 4 m roll is 24 m².
- Should I use a 4 m or 5 m roll?
- Whichever covers the room with the fewest drops. Rooms between 4 m and 5 m wide often fit a 5 m roll in one piece, saving a join and a lot of carpet.
- Do I include alcoves and bays?
- Yes. Plan from the overall rectangle, as the carpet comes off the roll as a rectangle. The cut-outs become offcuts, not savings.
Related resources
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