Carpet Calculator
Estimate how much carpet to buy from a roll, the offcut and the cost with underlay.
About the Carpet Calculator
Enter the room's length and width, the width of the carpet roll and the prices of carpet and underlay. The calculator works out how many drops (lengths) to cut, how much carpet to buy, the offcut and the total cost, with a diagram of the layout.
Carpet comes off rolls of a fixed width, so you buy whole roll-widths times the room length, not just the floor area. Underlay is bought for the room area.
The formula
Carpet = ⌈room width ÷ roll width⌉ × roll width × room length
Worked example
A 5 × 4.5 m room from a 4 m roll
- Drops: ⌈4.5 ÷ 4⌉ = 2, each 5 m long
- Carpet to buy: 2 × 4 × 5 = 40 m² for a 22.5 m² room
- Choosing a 5 m roll instead needs one drop, 25 m²
Things to keep in mind
- Assumes a rectangular room; add extra for alcoves, bay windows and stairs.
- Patterned carpet needs extra for matching the pattern at seams.
Questions people ask
Which way should the pile run?
Toward the main window or entrance, so seams are less visible.
Does the price include fitting?
Usually not; fitters charge per area.
Can I lay drops across the room instead?
Yes: swap length and width to compare, and pick the layout with less waste.