Carpet Calculator

Carpet formula

Runs = Room width / roll width, rounded up  (also try Room length / roll width)
Linear feet of roll = Runs x run length, using the orientation with less carpet
Order length = Linear feet x (1 + waste %), rounded up to a whole foot
Square yards = Order length x roll width / 9

Worked example

A 15 x 18 ft living room on a 12 ft roll: runs across the 15 ft width need 2 runs of 18 ft = 36 ft, while runs across the 18 ft length need 2 runs of 15 ft = 30 ft. Take 30 ft, add 10% for 33 ft. 33 x 12 = 396 sq ft, or 44 sq yd. The floor itself is 270 sq ft, or 30 sq yd, so 30 sq yd of pad. At $25 per sq yd the carpet costs $1,100.

On a 15 ft roll the same room needs one 18 ft run with no seam. With waste that is 20 ft, or 300 sq ft (33.3 sq yd), which saves 10.7 sq yd and the seam.

Quick reference

How to calculate carpet

Carpet comes off a roll, almost always 12 feet wide, so you buy a length of roll rather than the exact floor area. Divide the room's narrow dimension by the roll width and round up to get the number of runs, then multiply by the other dimension for the length of roll. A 10 by 12 foot room fits in one 10 foot run of 12 foot roll.

When a room is wider than 12 feet, check both directions. A 14 by 16 foot room needs two 16 foot runs (32 feet) laid one way but two 14 foot runs (28 feet) laid the other, and the leftover from the second run can fill a closet. Add 10 percent for trimming and seam allowance, or 15 percent for patterned carpet that must line up at seams.

Padding, seams and square yards

Carpet stores quote by the square yard, which is 9 square feet. Pad is cheap relative to carpet and can be pieced from scraps, so order pad for the floor area only. For most residential cut pile choose a 7/16 inch pad with 6 lb density; thicker or softer pads let the carpet flex and wear out the backing.

Plan seams to run with the length of the room and with the light from windows so they are less visible, and keep them out of doorways and traffic lanes. If a 13.5 or 15 foot roll width is offered in your style, it can remove the seam entirely in a bedroom or living room and often costs less overall despite the extra width.

Key facts

• Carpet is sold from 12 ft wide rolls; 13.5 and 15 ft widths are made for some styles and can eliminate a seam.
• One square yard is 9 sq ft. A 12 x 12 ft room is 16 sq yd of floor but needs about 18.67 sq yd of carpet.
• Residential cut-pile carpet needs a pad no thicker than 7/16 in with at least 6 lb density; berber and looped carpet needs 3/8 in or less at 8 lb.
• Seams should run the length of the room, parallel to the light from the main window so they cast no shadow, and never across a doorway.
• Rooms wider than the roll always need a seam, so ordering the run direction that leaves a strip of usable width cuts waste.

Frequently asked questions

Sources and references

• •Carpet installation guide: 12 and 15 ft rolls, seams and cushion (Shaw Floors)
• •CRI 105 Standard for Installation of Residential Carpet (Carpet and Rug Institute)
• •Carpet installation standards CRI 104 and 105 (Carpet and Rug Institute)