How Figure the Linear Feet of Carpeting Needed

Carpet rolls are usually 12 feet or 15 feet wide and carpeting is often sold by the linear foot. For example, if you purchase linear 20 feet from a roll that is 12 feet wide, you will have 240 square feet of carpet. Likewise, if you buy 450 square feet of carpet from a roll that is 15 feet wide, it is equivalent to buying 30 linear feet.

A common question when carpeting a room is how many linear feet to buy, given the dimensions of the room and the width of the carpet roll. Since the width of the carpet is fixed, you will almost always end up with excess. The goal is to end up with as little excess as possible and thus to find the minimum length of carpet needed. You can use the carpet calculator on the left to work out the correct length of carpet to buy, or use the equation given below.

Linear Feet Formula

To calculate the right number of linear feet, first measure the width and length of your rectangular space in feet. Convert any inches to the appropriate decimal. For example, 13' 6" = 13.5'. Call the longer dimension (the length) L and the shorter dimension (the width) W.

Next, divide the length and width of the room's floor by the width of the carpet roll in feet (R) and round up to the nearest whole number of feet. Call these numbers A and B respectively. In mathematical notation,

A = ⌈ L/R ⌉
B = ⌈ W/R ⌉

Now compare the two products A*W and B*L. The smaller of these two products is the number of linear feet of carpeting you need. If A*W is smaller than B*L, you will lay the rolls parallel to the width, the shorter side of the rectangle. If B*L is smaller than A*W, you will lay the rolls parallel to the longer side of the rectangle, the length. If A*W and B*L are equal, then it doesn't matter which arrangement you use.

Example 1: A room's width is W = 17.5 feet and its length is L = 26 feet. The width of the carpet roll is R = 12 feet. Thus the values of A and B are

A = ⌈ 26/12 ⌉ = 3
B = ⌈ 17.5/12 ⌉ = 2

and the values of A*W and B*L are

A*W = 3*17.5 = 52.5
B*L = 2*26 = 52

Thus, you need 52 linear feet from this roll. The total square footage is 52*12 = 624 sq.ft. When you lay this carpet you must roll it out parallel to the longer side of the room.

Example 2: Consider the same floor as described in Example 1, but this time the width of the carpet roll is R = 15 feet. The new values of A and B are

A = ⌈ 26/15 ⌉ = 2
B = ⌈ 17.5/15 ⌉ = 2

and the values of A*W and B*L are

A*W = 2*17.5 = 35
B*L = 2*26 = 52

Thus, you need 35 linear feet from this roll. The total square footage is 35*15 = 525 sq.ft. When you lay this carpet you must roll it out parallel to the shorter side of the room.

© Had2Know 2010