How to use the carpet calculator
- Measure the room’s length and width at the widest points, into door recesses and bay windows.
- Pick the roll width your store stocks. Most broadloom in North America is 12 ft wide; UK carpets usually come 4 m or 5 m wide.
- Leave the extra per drop at 6 in (15 cm) unless your fitter asks for more.
- Add the carpet price per square foot or square metre, and the underlay price if you need it.
- Read the length to buy and the layout, then take the shopping list to the store.
How the estimate is worked out
Carpet length = drops × (room length + trim allowance)
The same is done the other way round, and the shorter result is used
Carpet to buy = carpet length × (1 + extra %); area = length × roll width
Rooms narrower than the roll take a single drop with no seam. Wider rooms need two or more drops joined by seams, and the leftover strip from the last drop is waste. That is why carpet usually costs more than the floor area alone suggests.
Worked example
A 15 × 12 ft bedroom carpeted from a 12 ft roll, with 6 in extra per drop for trimming, 10% extra, carpet at $3 per sq ft and underlay at $0.60 per sq ft:
- Along the length: 12 ÷ 12 = 1 drop of 15.5 ft = 15.5 ft of roll. Along the width: 15 ÷ 12 = 2 drops of 12.5 ft = 25 ft. The first wins: 1 drop along the length, 0 seams.
- With 10% extra: 15.5 × 1.10 = 17.1 ft of a 12 ft roll, an area of 205 sq ft (22.7 sq yd).
- The room is 180 sq ft, so 12% of the carpet bought ends up as offcut.
- Carpet $613.80 plus underlay $118.80 gives $732.60.
Tips and common mistakes
- Keep the pile running one way. Every drop must be laid with the pile in the same direction, or the joined pieces will look like two shades. Do not turn an offcut sideways to fill a gap.
- Put seams where feet are not. Ask for seams away from doorways and main walkways, and parallel to the light from the main window so they are harder to see.
- Measure stairs separately. Stairs need treads, risers and nosings worked out step by step; fitters usually price them per stair.
- Check what the price includes. Some stores quote carpet only; others include underlay, gripper rods, door bars and fitting.
US, UK and Canada differences
US and Canadian retailers quote carpet per square foot or per square yard (9 sq ft), and the calculator shows square yards alongside square feet for that reason. Carpet pad is the North American term for the cushion underneath; in the UK and Ireland it is called underlay, carpet is sold per square metre, and the most common roll widths are 4 m and 5 m. Fitters in all three countries measure the room themselves before cutting, so treat this as a budget check.
Metric units and other countries
In metric mode, room sizes are in metres and the roll widths change to 3.66, 4 and 5 m. Wall-to-wall carpet is less common in hot climates such as South Asia and the Gulf, where area rugs on tile are popular; for a rug, the room area result tells you the size to look for. Type your local price per square metre.