How to Measure a Room for Carpet: Step-by-Step Guide

The formula, in one paragraph

Measuring a room for carpet is five steps. Measure the length and width, wall to wall, at the longest and widest points. Multiply them for the net area. Add 10% waste for the gross area. Divide the gross by 9 for the square yards. Round the square yards UP for the order. The example is a 12 by 10 foot room at 10% waste: net 120.00 sq ft, waste 12.00, gross 132.00, 14.67 sq yd, order 15 sq yd, 1 strip of 12.00 ft.

Step 1: Measure the length and the width

Measure the room wall to wall, at the longest point for the length and the widest point for the width. Use a tape measure, in feet, and measure twice: walls are rarely square, so use the longer measurement. The example room is 12 feet long and 10 feet wide.

Step 2: The net area

Multiply the length by the width for the net area: net = L × W. For the example room, 12 × 10 = 120.00 sq ft. The net area is the floor itself, not the order. For a 15 by 12 foot room, the net is 180.00 sq ft.

Step 3: The waste allowance

Add the waste: waste = net × w / 100, and gross = net + waste. The waste allowance is extra carpet for cuts, seams, and mistakes. Use 10% for a plain room: for the example room, 120.00 × 10 / 100 = 12.00 sq ft, so the gross is 132.00 sq ft. Use 15% or more for patterned carpet. With no waste, the gross equals the net: at 0% the gross is 120.00 sq ft, 13.33 sq yd, and the order is 14 sq yd.

Step 4: Square yards and the order

Divide the gross by 9: square yards = gross / 9. For the example room, 132.00 / 9 = 14.67 sq yd (exact 14.6667). Then round UP: order = ceiling of the square yards. The order is 15 sq yd — never the floor. For a 15 by 12 foot room, the gross is 198.00 sq ft, the square yards are 22.00 sq yd, and the order is 22 sq yd. For a 12 by 14 foot room, the gross is 184.80 sq ft, the square yards are 20.53, and the order is 21 sq yd.

Step 5: The cut plan — strips, linear feet, and leftover

A strip is one full-width piece. The number of strips is the room width divided by the roll width, rounded up: strips = ceil(W / roll width). The example room is 10 feet wide on a 12-foot roll, so it needs 1 strip. The linear feet are the room length times the strips: 12 × 1 = 12.00 ft. The roll area is the linear feet times the roll width: 12.00 × 12 = 144.00 sq ft. The leftover is the roll area minus the net area: 144.00 − 120.00 = 24.00 sq ft. A 14-foot-wide room on a 12-foot roll needs 2 strips: 24.00 ft, a roll area of 288.00 sq ft, 120.00 sq ft left over. On a 15-foot roll, the example room still needs 1 strip of 12.00 ft, but the roll area is 180.00 sq ft and the leftover is 60.00 sq ft.

Working backwards: the four reverses

For a gross of exactly 20 sq yd at 10 feet wide and 10% waste, the room length is 16.36 ft (exact 16.3636 ft): at 16.36 ft the gross is 179.96 sq ft, or 19.9956 sq yd. The waste for a gross of exactly 150 sq ft at 12 by 10 feet is 25%. The strip boundary on a 12-foot roll is 12 ft: 1 strip at 12 ft, 2 strips over it. From 15 linear feet of a 12-foot roll at 10% waste, the largest net room is 163.64 sq ft (exact 163.6364 sq ft). A 14-foot-wide room on a 15-foot roll needs only 1 strip, 12.00 ft, a roll area of 180.00 sq ft, and leaves 12.00 sq ft over.

What changes the answer

Three things move the order: the room size, the waste, and the roll width. A 15 by 12 foot room needs a gross of 198.00 sq ft and an order of 22 sq yd. The waste moves it by a square yard or two: 5% gives 126.00 sq ft and 14 sq yd, 15% gives 138.00 sq ft and 16 sq yd, and 20% gives 144.00 sq ft and 16 sq yd. The roll width changes the cut plan, not the square yards: on a 15-foot roll the leftover is 60.00 sq ft instead of 24.00.

What NOT to do

Do not order the net area: the example room needs 15 sq yd, not 13.33. Do not round the square yards down: 14.67 becomes 15, and 12.22 becomes 13. Do not measure at the shortest point. Do not forget the pattern: patterned carpet needs 15% waste or more. And do not confuse quantity with price: for the price, see the carpet cost calculator, and for the flooring decision, see carpet vs hardwood flooring.

That box is the whole formula.