Guide · For the trade
Carpet calculator for designers: how much carpet a room needs, in square yards
A carpet calculator does one division and one layout: the room's square feet divided by 9 gives net square yards, and the roll width (12 ft, 13 ft 2 in or 15 ft) decides how many full-width drops it takes to cover the room, which is the quantity actually ordered. A 12 by 12 room is 16 sq yd in one drop with no seam; a 20 by 20 room is 44.4 sq yd net and 53.3 sq yd ordered from a 12-foot roll, because the fill needs a second full-width drop. Through Interiors, you send the plan and we return the seam diagram and yardage with the quote.
This guide is for the designer or the junior who needs a quantity for a budget before the installer has measured, or wants to check the installer's number. It covers measuring, square feet to square yards, drops and fills by roll width, pattern repeat, stairs, waste, and what we need for the estimate. The broadloom carpet guide covers seams and where they go; this one covers the count.
How to measure a room for carpet
Measure the longest and widest points of the room wall to wall, including thresholds and any closet to be carpeted, and round up to the next half foot. Note the main doorway, because the pile runs away from it and the drops run with the longest dimension where they can. For a whole floor, list which rooms take the same carpet, because rooms in one style are cut from one roll and laid out together.
Square feet to square yards, and why the trade uses yards
Length times width in feet is square feet; divide by 9 for square yards. Mills sell by the square yard: a linear foot of a 12-foot roll is 1.33 sq yd, of a 13 ft 2 in roll 1.46 sq yd, of a 15-foot roll 1.67 sq yd. A client's 1,000 sq ft is 111 sq yd net before layout; keep both units on the estimate.
Drops and fills: the layout that sets the quantity
Carpet is cut in drops, full-width lengths of the roll laid side by side. A room narrower than the roll takes one drop; a room wider than the roll takes a main drop plus a fill, a strip cut from a second drop and seamed to the main. The fill runs the same direction as the main drop, because cut pile shades when turned, so the second drop is the room's length or half of it with a cross seam. That second drop is where the waste lives.
| Room | Net sq yd | From a 12 ft roll | From a 15 ft roll | Seams |
|---|---|---|---|---|
| 10 by 12 | 13.3 | 13.3 (one 10 ft drop) | 16.7 (one 10 ft drop) | None |
| 12 by 12 | 16 | 16 (one 12 ft drop) | 20 (one 12 ft drop) | None |
| 12 by 15 | 20 | 20 (one 15 ft drop) | 20 (one 12 ft drop) | None |
| 14 by 16 | 24.9 | 32 (16 ft drop plus 8 ft drop for two 2 ft fills) | 26.7 (one 16 ft drop) | One on 12 ft, none on 15 ft |
| 15 by 20 | 33.3 | 40 (20 ft drop plus 10 ft drop for two 3 ft fills) | 33.3 (one 20 ft drop) | One on 12 ft, none on 15 ft |
| 20 by 20 | 44.4 | 53.3 (two 20 ft drops) | 50 (20 ft drop plus 10 ft drop for two 5 ft fills) | One either way |
Add 3 to 6 inches to every drop for trim. The 14 by 16 room is the case to remember: 32 sq yd with a seam from a 12-foot roll, 26.7 sq yd with none from a 15-foot roll. When a style comes in both widths, as many Prestige Mills and Stanton wool lines do, we lay it out both ways.
Pattern repeat adds a repeat per drop
A patterned carpet has to match across the seam, so every drop after the first gets one extra pattern repeat in its length to allow the installer to align it. A 36-inch repeat on a room needing three drops adds 6 feet of length, or 8 sq yd on a 12-foot roll. The repeat is on the spec sheet; the pattern repeat guide covers set-match and drop-match.
Stairs: count the risers, not the square feet
A straight stair of 13 risers with 11-inch treads and 7 1/2 inch risers uses about 20 inches of carpet per step with the nosing wrap: 13 steps is about 22 feet, plus a foot at each end, 24 feet of runner. Cut lengthwise from a 12-foot roll, one 24-foot cut yields four 36-inch or five 27-inch runners, 32 sq yd, so the hall and bedside runners come from the same cut and the stair and hall are estimated together. Landings and winders are measured as small rooms. The measuring for carpet guide covers the site measure.
Waste, and what the 10 percent rule misses
The old rule adds 10 to 15 percent to net square feet. It is right on average and wrong in every particular: a 12 by 12 room on a 12-foot roll has zero waste, a 14 by 16 room has 29 percent. Use the layout, which is what we send. Remnants from a whole-house order get bound into bath mats or kept as attic stock for a repair, because dye lots do not repeat.
What we need to produce the estimate
- The plan, dimensioned, or a sketch with wall-to-wall measurements, door and window positions, and the closets to be carpeted.
- Which rooms take which style, so same-style rooms are laid out from one roll.
- The style and color, so we use its actual roll width and pattern repeat.
- Stairs: number of risers, tread and riser dimensions, stair width, runner or wall-to-wall, and any landings.
With that, the seam diagram and yardage come back with the quote in a day or two. The installer confirms the numbers at the site measure and the order is placed from it, in one dye lot. The ordering broadloom guide covers what happens after the yardage is set.
Questions designers ask
How do I calculate how much carpet I need?
Room length times width in feet, divided by 9, is the net square yards. Then lay the room out in full-width drops from the style's roll width and add a drop for any fill; the total length of the drops times the roll width, divided by 9, is the ordered yardage. Add one pattern repeat per extra drop on a patterned style.
How much carpet does a 20 by 20 room need?
400 sq ft net, which is 44.4 sq yd. From a 12-foot roll, two 20-foot drops, 53.3 sq yd with one seam; from a 15-foot roll, a 20-foot drop plus a 10-foot drop cut into two 5-foot fills, 50 sq yd.
What does it cost to carpet a 12 by 12 room?
Net pricing is quoted to trade accounts, so this is the quantity: 16 sq yd, one 12-foot drop from a 12-foot roll, no seam, plus 16 sq yd of pad and the labor for one room. The price moves with the fiber and construction; the yardage does not.
What does 1,000 sq ft of installed carpet involve?
111 sq yd net and usually 125 to 135 sq yd ordered across several rooms, with pad to match and a day or two of installation. The layout across the rooms, not the square footage, sets the final number.
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