How to Measure for Carpet in the UK (Roll Widths Explained)

Quick answer: Measure the room’s longest and widest points in metres, including bays and doorways, and add at least 10 cm to each. UK carpet comes on rolls usually 4 m or 5 m wide, so you buy a length off the roll: a 3.8 × 4.6 m room needs 4.7 m from a 4 m roll (18.8 m²).

Carpet is the one floor covering where the room’s area is not what you pay for. Because it is cut from a fixed-width roll, the shape of the room and the way the roll is laid decide how much you buy. This guide walks through measuring, choosing the roll width and avoiding waste. It is part of the home measuring guides collection.

Table of Contents

Why is carpet measured differently from other flooring?

Carpet is sold by the linear metre off a roll of fixed width, so you pay for a rectangle, not for the room’s exact floor area. In the UK, most broadloom carpet comes in 4 m or 5 m widths, although the widths on offer vary by manufacturer and range. Whatever width you choose, the retailer cuts a length to order and charges for length × roll width.

That is why a room of 17.48 m² can cost you 18.8 m² or 19.5 m² of carpet depending on which roll is used and which way round it goes:

The 3.8 m side fits across a 4 m roll, so Option A wastes less than laying a 5 m roll the other way. Always check both orientations.

If you want the room’s true floor area as well, for example to compare with a vinyl or laminate quote, the guide on measuring a room in square metres covers L-shapes and awkward corners.

What do you need to measure for carpet?

A metric tape measure (5 m or longer) or a laser measure.
Paper and pen for a sketch plan with doors, bays, alcoves and radiators marked.
The roll widths of the carpet you are considering, from the retailer’s product page or sample label.

How do you measure a room for carpet step by step?

Clear what you can and sketch the room. Mark which wall the door is on and any bay, alcove or chimney breast.
Measure the longest point. Go wall to wall at floor level, and include the full depth of any bay window or recess, because the carpet has to reach into it.
Measure the widest point. Again include alcoves and recesses. Measure in two or three places, as walls are often out of parallel.
Include the doorway. Measure to the middle of the door frame (under the closed door), where the door bar or threshold strip will sit.
Add at least 10 cm to each measurement. This allowance covers trimming against skirting boards and small irregularities in the walls.
Match to a roll width. If either adjusted measurement is no more than the roll width, that dimension can go across the roll and the other becomes the length you order.

A room with a bay: the 4.6 m length includes the bay, the 10 cm allowance takes it to 4.7 m, and the 3.6 m width fits across a 4 m roll.

Use a metric tape if you can. Carpet is priced per square metre in UK shops, and converting feet and inches adds a step where mistakes creep in. The guide to reading a tape measure explains the metric markings if you are used to inches.

How much extra carpet should you allow?

Add at least 10 cm (about 4 in) to both the length and the width. Carpet retailers commonly recommend this so the fitter can trim the edges neatly into the gripper. There is no single percentage that suits every room, because the real waste depends on the roll width, the room shape and whether a join is needed.

Patterned and striped carpets need more. The pattern has to line up at any join and look square to the main wall, so a fitter may need an extra pattern repeat (often shown on the product label) on the length.

Carpet length calculator (adds 10 cm each way)

m× m =Buy 4.70 m off a 4 m roll (18.80 m²)

Worked example: a bedroom measures 3.42 m by 3.95 m at its widest points. Adding 10 cm gives 3.52 m by 4.05 m. The 3.52 m side fits across a 4 m roll, so you order 4.05 m of carpet: 4 × 4.05 = 16.2 m². Laid the other way, a 5 m roll would need 3.52 m of length, or 17.6 m², so the 4 m roll is the better buy.

How do you measure doorways, bays and alcoves?

Measure into every space the carpet must reach, because the piece is cut as one rectangle that covers them all. A few specific rules:

Doorways: measure to the centre of the door when it is closed. Gripper is not fitted across thresholds, so the edge is finished with a door bar suited to the floor on the other side (carpet, vinyl, laminate or tiles).
Bay windows: measure to the deepest point of the bay. The offcuts either side of the bay are waste, which is normal.
Alcoves beside a chimney breast: measure to the back wall of the alcove, not to the face of the breast.
Radiators and pipes: ignore them for measuring; the fitter cuts around pipes on site.

When does a carpet need a join?

A join (seam) is needed when both of the room's adjusted measurements are wider than the widest roll available. For a carpet sold only in 4 m and 5 m widths, that means a room measuring more than 4.9 m in both directions, because adding 10 cm takes it past 5 m.

Joined pieces must be cut so the pile runs the same way in each, otherwise they reflect light differently and look like two shades. Plan the join away from doorways and main walkways where it will be most visible and take the most wear. For big or open-plan rooms, most retailers will produce a cutting plan from your measurements, and a professional measure is worth considering.

How much underlay and gripper do you need?

Underlay is worked out from the room's floor area; gripper from its perimeter, minus doorways. Underlay is butted together rather than overlapped, so it does not need the same roll-width allowance as carpet. For gripper, add up the length of every wall where carpet will be fitted and subtract the width of each doorway.

Example for the 3.8 × 4.6 m room with one 0.8 m doorway: underlay 3.8 × 4.6 = 17.48 m² (buy the next whole roll size up); gripper (3.8 + 4.6) × 2 − 0.8 = 16.0 m.

How do you measure stairs and landings for carpet?

Stairs are measured by adding the depth of each tread and the height of each riser, then multiplying by the number of steps. Landings are measured like a small room and often cut from the same roll. The separate guide on measuring stairs for carpet covers straight flights, winders and bullnose steps in detail.

Common mistakes to avoid

Ordering by floor area. Telling a shop "my room is 15 m²" does not work for carpet; give them the length and width so they can fit the room to a roll.
Measuring only to the face of the bay or alcove. The carpet will come up short and cannot be patched invisibly.
Forgetting the doorway. Without the extra few centimetres under the door, the edge ends short of the door bar.
Not checking the other orientation. Always test both ways round against every roll width offered.
Using different pieces with the pile in different directions. Even plain carpets look patchy if pieces are turned.

Frequently asked questions

What width does carpet come in UK?

Most carpet in the UK is sold in 4 m and 5 m roll widths, though the widths available depend on the manufacturer and range. Check the product page before you work out your order.

How much extra carpet should I order?

Add at least 10 cm to both the length and the width of the room. Patterned carpet may need an extra pattern repeat on the length.

Do you measure carpet into the doorway?

Yes. Measure to the centre of the door when closed, where the door bar will sit, so the carpet reaches the threshold.

How many square metres of carpet do I need for a 4 x 4 m room?

With 10 cm added each way the room is 4.1 × 4.1 m, which is too wide for a 4 m roll, so you would buy 4.1 m off a 5 m roll: 20.5 m².

Should I measure in feet or metres for carpet?

Metres. UK carpet is sold in metre roll widths and priced per square metre, so measuring in metres avoids conversion errors.

Sources

Online Carpets: How to measure a room for carpet or flooring (roll widths, 10 cm allowance, door bars)
Flooring Hut: What widths do carpets come in? (roll widths, joins and pile direction)