Carpet calculator

The formula

1. Drops: the room's side across the roll ÷ the roll width, rounded up. Each drop is a full roll width; the last one may be only partly used, and a seam joins each pair.
2. Drop length: the room's other side plus the trim allowance, 3 in at each wall.
3. Linear feet: drops × drop length. That is what the shop cuts from the roll.
4. Square yards ordered: linear feet × roll width ÷ 9, rounded up to the whole square yard, as carpet is sold. That is the quantity the carpet is priced on. Compare it with the room's own area (length × width ÷ 9): the difference is the waste.
5. Pad: the room's area, rounded up to the whole square yard.
6. Installed price: carpet on the square yards ordered, pad and installation on the room's floor, each at a low and a high rate.

Worked example

A 22 × 16 ft living room on a 12 ft roll, with the drops running along the 16 ft side. 22 ÷ 12 = 1.8, so 2 drops and one seam; each drop is 16 ft plus 6 in of trim, 16 ft 6 in. That is 33 linear feet of roll, 33 × 12 = 396 ft², or 44 yd² ordered for a room of 352 ft² (39.1 yd²): 11% waste. Running the drops the other way would take 2 drops of 22 ft 6 in, 45 linear feet, 60 yd². The pad is 40 yd². At Homewyse's rates (the carpet less its 6.75% overage) the job costs $1,269 to $1,669 for the carpet, $220 to $252 for the pad and $443 to $907 to install: $1,931 to $2,829.

A room just over 12 ft wide is where the roll width matters most: a 13 × 15 ft room on a 12 ft roll needs a second drop for one foot of floor, while a 15 ft roll covers it in one piece. In metric, a 5 × 4 m room on a 4 m roll is one drop of 5.15 m, 20.6 m² for 20 m² of floor.

Seams and nap

• Seams: each drop after the first adds one. Try both directions and both roll widths: the calculator shows the other direction under the answer.
• Nap and pattern: every drop must run the same way, so a narrow strip cannot be turned to fill a gap. A patterned carpet also needs extra length on each drop to match the pattern (CRI 105, §5.3); add it to the trim allowance.
• Several rooms: an installer plans the whole floor at once, and an offcut from one room can fill a closet or a hall. The calculator works one room at a time, so its total is an upper bound for a house.

Every room at once

FloorGen's Schedules and budget panel (in the account menu) lists each room's floor area and multiplies it by rates you enter in the Budget section. See materials estimate from a floor plan for a worked house.