How much carpet do I need for my room?
You have a room size and want to know how many metres to buy off the roll.
You need a length of carpet off a roll, not a number of square metres. Take the longest length of the room, add about 10cm at each end for trimming, and check the room's width fits inside one roll width. The amount you pay for is that length multiplied by the full roll width, whatever the floor area works out as.
Written for: Written for anyone about to order carpet who wants to know the length to ask for, not just the floor area.
Floor area is not the number you buy
Most online calculators multiply length by width and stop there. That tells you the size of your floor, which is useful for underlay and for comparing quotes, but it is not what comes off the roll. Carpet at our warehouses is cut from rolls of a set width, usually four metres, and you buy a length of that roll.
So a bedroom of 3.2m by 3.6m has a floor area of 11.52 square metres, but if it is cut from a 4m roll you will pay for 4m wide by about 3.8m long once trimming is allowed for. That is 15.2 square metres of carpet. The difference is not a trick, it is the offcut, and a good fitter will tell you whether it is big enough to be useful elsewhere.
Worked examples for common room sizes
These assume a single piece from a 4m roll, with 10cm added at each end for trimming. Your own quote will be worked out from your actual measurements and from the rolls genuinely in stock on the day, so treat these as a way of checking the maths rather than a price.
- Box room, 2.4m x 2.7m: order 4m x 2.9m, which is 11.6 square metres of carpet for 6.5 square metres of floor. The offcut is wide enough for a landing or a small hallway.
- Double bedroom, 3.5m x 4.0m: turn the carpet so the 3.5m side runs across the roll, order 4m x 4.2m, 16.8 square metres.
- Living room, 4m x 4m (a common search): the width sits exactly on the roll edge with nothing to trim, so ask for the 4m side to run along the roll and order 4m x 4.2m. If any wall is out of square, the fitter may need more.
- Room of 12ft x 12ft: that is about 3.66m square. Order 4m x 3.9m, roughly 15.6 square metres of carpet.
- Room of 10ft x 10ft: about 3.05m square. Order 4m x 3.3m, roughly 13.2 square metres, which is exactly the size where a remnant is often the cheapest answer.
Converting common imperial room sizes
| Room in feet | Room in metres | Floor area | Typical length from a 4m roll |
|---|---|---|---|
| 9ft x 9ft | 2.74m x 2.74m | 7.5 m2 | 4m x 2.95m |
| 10ft x 10ft | 3.05m x 3.05m | 9.3 m2 | 4m x 3.3m |
| 12ft x 12ft | 3.66m x 3.66m | 13.4 m2 | 4m x 3.9m |
| 12ft x 15ft | 3.66m x 4.57m | 16.7 m2 | 4m x 4.8m |
Lengths include about 10cm for trimming at each end and assume the room fits within one roll width.
When the room is wider than the roll
If a room is 4.3m by 5m, a 4m roll will not cover the width. You then either buy a 5m wide roll where the range comes in that width, or you buy extra length and join a strip down one side. The join means buying almost twice the carpet for a room only slightly too wide. This is the single biggest reason two quotes for the same room can differ, so always ask how the carpet will be laid out.
Pile direction matters too. Carpet has a nap, and every piece in a room has to run the same way or the colour looks different under light. A fitter cannot simply turn an offcut sideways to fill a gap.
Hallways, landings and stairs
Stairs are counted differently. Count the treads and risers and measure the width of the flight. A straight staircase is often cut as one long strip, and a flight with winders takes more because each winder is shaped. Bring the numbers in and the team will tell you whether a length from the roll, a roll end or a remnant will do it.
A hallway and landing are often best planned together, because the offcut from one can sometimes cover the other if the pile runs the right way.
Let us check it before you buy
Send your room sizes through the form and we will work out lengths against what is actually on the racking in Maidstone and Gillingham. Where it helps, we offer onsite measuring in most Kent areas, which removes the guesswork completely.
Useful pages for this job
Common questions
- How many square metres of carpet do I need for a 4m x 4m room?
- The floor is 16 square metres, but allowing for trimming you would normally order a 4.2m length from a 4m roll, which is 16.8 square metres of carpet.
- Should I add extra for mistakes?
- The 10cm trimming allowance at each edge covers normal fitting. You do not need to add a further percentage unless the room has unusual angles.
- Is underlay bought to the same size?
- Underlay only needs to cover the floor itself, so it is usually worked out from the floor area rather than the carpet length.
- Can you work it out for me?
- Yes. Send the room sizes and the team will calculate the lengths against the rolls in stock, free and with no obligation.
- Do you fit, or is this a job for me?
- Either. We work with trusted, fully vetted local fitters across Kent, and plenty of customers fit smaller rooms themselves and buy supply only.
Send the sizes, we will do the sums
Tell us each room and we will come back with the lengths and a price from stock.