How Much Carpet Do I Need?

Why you order more than the floor area

Carpet comes in long rolls of a fixed width, commonly 4 m or 5 m, and sometimes 2 m, 3 m or 3.66 m (12 ft). It is cut to length across the full width of the roll, and you pay for what you take. A 4 m by 3 m room is 12 m² of floor, but a 4.1 m cut from a 4 m roll is 16.4 m² of carpet.

The difference is offcut. It is not wasted by mistake: it is a result of the room not matching the roll width. It can be a bigger share of the order in a small room.

Measure the room

Measure the length and width of the room at the widest points, from wall to wall, and include doorways and alcoves that will be carpeted. Measure each side twice and write the figures on a sketch. For an L-shaped room, split it into rectangles and measure each one.

Carpet is trimmed to fit at the walls, so add an allowance on each edge. 50 mm per edge is a typical starting point, and your fitter may want more. The allowance is added to both ends of each measurement, so 50 mm per edge makes a 4 m room 4.1 m.

Count the strips, both ways round

Strips can run along either side of the room. For each way, work out how many roll widths are needed to cover the other side, and multiply by the length of the strip. A 4 m by 3 m room with a 4 m roll needs one strip if you run along the 4 m side, because 3.1 m fits inside the roll. Running along the 3 m side needs two strips, because 4.1 m is wider than the roll.

Choose the layout that uses less carpet. Your fitter may choose differently, for example to run the pile in the best direction for the room, so ask before you order.

• Along the 4 m side: 1 strip × 4.1 m = 4.1 m, so 16.4 m² from a 4 m roll
• Along the 3 m side: 2 strips × 3.1 m = 6.2 m, so 24.8 m² from a 4 m roll

Seams and patterned carpet

A room wider than the roll in both directions needs a seam. A 6 m by 5.5 m room from a 5 m roll needs two strips whichever way they run. Running along the 5.5 m side is the better layout: two 5.6 m strips make 11.2 m, which is 56 m² of carpet for 33 m² of floor, with one seam.

Patterned carpet needs extra length at each seam so the pattern matches. The pattern repeat is on the label, and one repeat per extra strip is a common allowance. Ask your fitter where the seam should go: they are usually best away from doorways.

Underlay, extras and stairs

Underlay is bought for the floor area, not the carpet order, so buy 12 m² for the 4 m by 3 m room. Gripper rods, door bars and fitting are separate costs.

Stairs and landings are measured and priced differently from rooms, so ask a fitter to measure them. Get the fitter to check your room measurements before you order, since a small error is expensive when carpet is cut to length.