Carpet calculator: how much carpet to buy from the roll
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| Rooms or stairs? | Rooms |
| Rooms | Bedroom: length 4.5 m, width 3.6 m, doorway widths 0.8 m, door bars 1 |
| Pile direction | Whichever buys least |
| Roll widths you can buy | 4, 5 m |
Order: 18.0 m² of carpet (4 m × 4.5 m)
| Result | Value |
|---|---|
| Carpet to buy | 18 m² |
| Floor covered | 16.2 m² |
| Offcut | 1.8 m² |
| Seams | 0 |
| Gripper | 15.4 m |
| Door bars | 1 |
| Room | Strips (width × length) | Bought | Seams |
|---|---|---|---|
| Bedroom | 4 m × 4.5 m | 18 m² | 0 |
Show the working
- Bedroom: 4.5 × 3.6 m = 16.2 m²; strips run along the length (4.5 m) to cover 3.6 m: 4 m × 4.5 m = 18 m² bought, 0 seams
- Bedroom gripper: 2 × (4.5 + 3.6) − 0.8 m of doorways = 15.4 m
- Total: 18 m² bought for 16.2 m² of floor (1.8 m² offcut)
How it works
- Rooms: strips of the roll width run one way (the pile must run the same way on every piece); enough strips to cover the other way; each strip is cut to the room length + trim
- Carpet bought = strip widths × cut length; the direction that buys least wins unless you fix the pile direction
- Seams = strips − 1; gripper = room perimeter − doorways; underlay rolls = floor area ÷ roll size, rounded up
- Stairs: runner length = treads × (tread depth + nosing wrap) + risers × riser height + trim, cut from the narrowest roll that covers the width
Carpet is sold off the roll by the linear metre at the roll width, so a room slightly wider than 4 m often needs a 5 m roll or a seam.
Fitters usually add a little length to trim in at each wall; add it under More settings.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Roll widths you can buy | 4, 5 m | Common UK size Not yet checked against the source | From your product brief v2 FL1 (4 m or 5 m rolls). Researcher to confirm against UK carpet retailers. |
| Underlay roll size | Enter from the bag, pack or tin | Common UK size Not yet checked against the source | From your product Enter from the underlay roll. |
| Gripper strip length | Enter from the bag, pack or tin | Common UK size Not yet checked against the source | From your product Length of one gripper strip, from the pack. |