How to use the carpet calculator
Carpet is sold off a roll of fixed width, typically 12 ft in the US and 4 m or 5 m in the UK and Europe. You order a length of that roll, so the amount you pay for depends on how the strips fit the room, not only on the floor area. This calculator tries the drops in both directions, picks the one that uses the least carpet, and shows the seams, waste, underlay and gripper that go with it.
- Choose units. US mode works in feet and inches and reports square feet and square yards. Metric mode works in metres and millimetres and reports square metres.
- Enter the room at its widest points, including bays and the space under door frames. For an L-shaped room, work out each rectangle separately, or get the total from the square footage calculator.
- Enter the roll width of the carpet you like, and a trim allowance for each drop. Add the pattern repeat if the carpet has one.
- Pick a lay direction, or leave it on Best. Add the total width of the doorways so the gripper length is right, and a price if you want a cost.
Carpet formulas
Drops = ⌈room width ÷ roll width⌉ (laying along the length)
Drop length = room length + trim allowance, rounded up to the pattern repeat
Carpet to buy = drops × drop length (linear) × roll width (area)
Seams = drops − 1 · Waste = area bought − floor area
Underlay = floor area × (1 + waste %) · Gripper = perimeter − doorway widths
The calculator runs the same sums with the drops across the width and keeps the smaller result unless you fix the direction. It assumes full-length strips without reusing offcuts, which is the safe figure for ordering. One square yard is 9 ft², or 0.836 m².
| Market | Common roll widths | Usually priced per |
|---|---|---|
| US and Canada | 12 ft, 13.5 ft, 15 ft | yd² or ft² |
| UK and Ireland | 4 m, 5 m, some 3.66 m | m² |
| Europe | 4 m, 5 m | m² |
| Carpet tiles | 50 × 50 cm, 24 × 24 in | box or m² |
For carpet tiles there are no drops to fit, so treat them like any other modular floor in the tile calculator.
Worked examples
A 14 × 18 ft living room
The floor is 252 ft², or 28 yd². On a 12 ft roll, drops along the 18 ft length need two strips to cover the 14 ft width, 37 ft of roll or 49.3 yd². Turning them across the room needs two 14.5 ft drops, 29 ft of roll or 38.7 yd², with one seam and about 10.7 yd² of waste. Switch to a 15 ft roll and a single 18.5 ft drop covers the whole room with no seam: 30.8 yd², only 2.8 yd² more than the floor. Underlay with 5% extra is about 29.4 yd², and the gripper runs 61 ft around the 64 ft perimeter after a 3 ft doorway.
A 4.2 × 3.6 m bedroom
The floor is 15.12 m². On a 4 m roll, a single drop along the 4.2 m length covers the 3.6 m width, so with 100 mm of trim you buy 4.3 m of roll, or 17.2 m², with no seam and about 2.1 m² of waste. Laying it the other way would need two drops and 29.6 m². Underlay comes to 15.9 m², and the gripper is 14.8 m after an 800 mm doorway.
Who this calculator helps
- Interior designers specifying broadloom carpet and checking a flooring quote.
- Architects putting carpeted areas into a cost plan or finishes schedule.
- Flooring contractors deciding between roll widths and planning where seams fall.
- Homeowners and landlords budgeting a bedroom or stair-and-landing refresh before visiting a showroom.
Practical tips
- Measure every room at its longest and widest points and into the doorway to halfway under the door.
- Ask the shop for the next roll width up when a room is just over one roll wide; a seamless room often costs about the same.
- Order every strip for one room from the same roll and dye lot, and lay them with the pile running the same way.
- If you are choosing a rug instead of wall-to-wall carpet, the rug size guide gives the right size for the layout.
Want the client to see the new carpet before you order? Try different flooring on a photo of the room with Flooring.
