How Much Carpet Do I Need? Measuring for Carpet

Why you pay for more than your floor area

In the UK, carpet is usually sold from rolls 4m or 5m wide, and you buy a length off the roll. Whatever the shape of your room, you pay for the full roll width × the length you need.

For example, a bedroom 4.5m × 3.6m has a floor area of 16.2m². Add about 100mm to each dimension for trimming (4.6m × 3.7m). The 3.7m width fits within a 4m roll, so you buy 4m × 4.6m = 18.4m². You're paying for about 2m² more than your floor area – that's normal.

Choosing the best roll direction

It's worth checking both ways round:

4m roll across the 3.7m side: 4 × 4.6 = 18.4m².

5m roll across the 4.6m side: 5 × 3.7 = 18.5m².

Here the 4m roll wins slightly. On other rooms the difference can be much bigger. The Carpet Calculator checks both orientations and both roll widths for you.

When you need a seam

If your room is wider than the roll (more than about 5m), you'll need two pieces joined with a seam. Good fitters place seams away from doorways and walkways and run the pile the same way on both pieces. Sometimes the offcut from the first piece can fill the gap, so ask your fitter to plan the layout.

How to measure

• Measure the longest length and widest width of the room, into door recesses and bay windows.
• Measure to the halfway point under each door, where the door bar will go.
• Add about 100mm to each dimension for trimming.
• For L-shaped rooms, measure each section, but remember that one piece covering the whole rectangle is often simplest – check with your fitter.
• Note the number of doorways for door bars.

Underlay, gripper and door bars

Underlay is priced per m² of floor area (not roll area), plus about 5%. Good underlay makes cheaper carpet feel better and last longer. If you have underfloor heating, choose a low-tog underlay – a common guide is keeping the combined tog of carpet and underlay at 2.5 or below so heat can get through.

Gripper rods go around the edge of the room, except across doorways. Measure the perimeter and subtract door widths.

Door bars finish the edge where the carpet meets another floor.

Stairs

Stair carpet is measured differently. Allow around 0.5m of carpet per stair (tread plus riser plus nosing) at the width of the stairs. A typical 13-step UK staircase needs about 6.5m, plus extra for landings and winders. Stair runners are sold in narrower widths.