Carpet Size Calculator
Enter the room length and width, the roll width the shop sells and the price per square metre or foot. The calculator works out how much to cut from the roll, the waste, seams, underlay and gripper rod.
- Cut from the roll
- Seams and waste
- Underlay and gripper
Measure at the widest points, into door recesses and bay windows. Pick a roll width in the same unit as the room.
Carpet is cut from a roll of fixed width. You pay for the full roll width times the length cut, so a 3 × 4 m room on a 4 m roll needs 3.1 m cut, about 12.4 m², even though the floor is 12 m². Wider rooms need two strips and a seam.
Carpet size chart
Metric rolls, 10 cm trim per strip. Search for a room.
| Room (m) | Floor (m²) | 4 m roll: cut | 4 m roll: m² | 5 m roll: cut | 5 m roll: m² |
|---|---|---|---|---|---|
| 3 × 3 | 9 | 3.1 | 12.4 | 3.1 | 15.5 |
| 4 × 3 | 12 | 3.1 | 12.4 | 3.1 | 15.5 |
| 4 × 4 | 16 | 4.1 | 16.4 | 4.1 | 20.5 |
| 5 × 4 | 20 | 5.1 | 20.4 | 4.1 | 20.5 |
| 4.5 × 3.5 | 15.75 | 4.6 | 18.4 | 3.6 | 18 |
| 6 × 5 | 30 | 10.2 | 40.8 | 6.1 | 30.5 |
Figures in m². A roll that matches the room width keeps waste and seams down.
Room width and carpet
Room 5 m long. Slide the width.
Strips from the roll are laid across the room. The pale area is trimmed off and wasted.
How to measure for carpet
Room to roll. Step through it.
Measure the room
Widest points.
For feet, ask for the roll width in feet: US carpet usually comes in 12 or 15 ft rolls.
4 m, 5 m or broadloom
Roll widths. Compare them.
The most common UK width.
For wider rooms.
US standard.
Stairs are measured separately: about 0.5 m of carpet per step on a straight flight.
Before ordering
Carpet checks. Tick each item.
Tick each item as you go.
Seams should run toward the main window and away from doorways, where they wear and show least.
What you get
Carpet order. Each tile explains one result.
From the roll.
m² or ft².
Trim and offcut.
Perimeter.
At your price.
Underlay is usually sold in rolls of about 15 m² and butted, not overlapped, so order a little over the floor area.
Frequently Asked Questions
No question matches that search.
How much carpet do I need?
Strips of the roll width across the room, plus 10 cm trim each end.
How do I work out carpet for a 4 × 3 m room?
On a 4 m roll, cut 3.1 m: about 12.4 m².
Why do I pay for more than the floor area?
Carpet is cut from a fixed roll width, so the offcut is paid for too.
What width does carpet come in?
4 m and 5 m in the UK, 12 ft and 15 ft in the US.
How much underlay do I need?
The floor area plus about 5%.
Where should carpet seams go?
Away from doors and along the main light direction.
How much gripper rod do I need?
The room's perimeter, less doorways.
Buy the right length of carpet
Match the roll to your room, cut it with a little trim and add underlay and gripper. You avoid paying for waste you did not need.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.