How Much Carpet Do I Need?

Carpet is the odd one out among floor coverings. Tile and laminate are sold by the box and you buy enough to cover the area. Carpet comes off the roll at a fixed width - 12 ft (3.66 m) in most of the world - and you buy it by the running length. So “how much carpet do I need” is really “how many linear yards of this roll width”, and that depends on how the strips fall in the room.

The three numbers you need

1. Your room sizes - length × width for each room, measured at the widest points.
2. The roll width - 12 ft / 3.66 m as standard; see standard carpet roll widths.
3. A wastage allowance - extra for trimming, pattern match and pile direction.

The method

strips     = ceil( room width ÷ roll width )
linear run = strips × room length
to buy     = linear run × wastage   (summed across rooms)

If the room is no wider than the roll, that is one strip and no seam - you just order the room length. If it is wider, you need a second strip and a seam, and the leftover of that strip is carpet you still pay for. That is the price of a fixed roll width, and it is why you work in running length rather than loose square footage.

Worked example: a 12x12 room

A 12 ft × 12 ft bedroom on a 12 ft roll:

1. The room is exactly the roll width, so it is one strip, no seam.
2. Linear run: 12 ft = 4 linear yards.
3. Add 10% wastage: 4 × 1.10 ≈ 4.4 linear yards to order.

A 15 ft × 12 ft living room on the same roll runs the strip the 15 ft way (still one strip, because 12 ft ≤ the roll), so you order 15 ft = 5 linear yards plus wastage. Only when the room is wider than 12 ft do you pick up a second strip.

The carpet calculator does this for every room at once - enter your sizes and roll width, pick a wastage allowance, and it returns the linear yards to buy, the floor area in square feet and square yards, and the seams.

Room-size quick reference

Linear run on a 12 ft (3.66 m) roll, before wastage, for rooms up to the roll width:

Rooms wider than the roll (over 12 ft / 3.66 m on one side) need a second strip and a seam - the calculator works those out for you.

Don’t forget the stairs and the extras

• Stairs are a continuous runner, not an area - count the steps and measure the tread and riser. See how to measure stairs for carpet.
• Underlay is sold by the area and sized from your floor area, not the broadloom run.
• Gripper rod, door bars and fitting are priced separately - see how much carpet costs.

Why you should not order tight

Keep an offcut for repairs, and buy a room’s carpet in one go from one batch - colour can vary slightly between production runs, so topping up later risks a visible mismatch. Rounding up the wastage gives you that margin.