How Much Carpet Do I Need for a Room?

What you need

A tape measure, a pencil and the room empty enough to reach the walls. You will also need the carpet's roll width — most carpet comes on a 12 ft (3.66 m) roll, but check, because a 15 ft roll changes the maths completely.

Step 1 — Measure the room

Measure the length and the width, wall to wall, at floor level, in both directions. Note the longest wall: the roll runs along it. Measure doorways and alcoves separately — carpet is cut to the room's shape, and a bay window is its own small piece, not an excuse to round the whole room up.

Step 2 — Work out the strips

Divide the room's width by the roll width and round up: that is the number of strips. One strip runs the full length of the room. A room narrower than the roll needs one strip; a room wider than the roll needs two or more, with a join. Joins should run away from the main light source and never across a doorway if you can avoid it.

Step 3 — Add wastage and order

Add 10% wastage for pattern matching and trimming, then order by the square yard — carpet is sold by the square yard, not the square foot. The carpet calculator does the conversion for you: enter the room size and the roll width, and it gives you the area in square yards, the number of strips and the linear length to order.

Underlay and gripper rods

Most carpets need underlay — it adds comfort, insulation and life to the carpet — and gripper rods around the edges to hold the carpet in place. Order the underlay for the same area as the carpet, and count the gripper rods by the room's perimeter, not by its area. Check the old rods and underlay before you reuse them: sound rods can stay, but flat or damp underlay should be replaced.

Worked example

A room 12 ft × 10 ft is 120 ft² (11.15 m², or 13.33 yd²). With a 12 ft roll and 10% wastage, you need 14.67 yd² of carpet. The room is 10 ft wide, so one strip covers it, and the linear length to order is 13.2 ft. Those are exactly the numbers the carpet calculator gives you.

Common mistakes

• Ordering by the square foot. Carpet is sold by the square yard. Ordering square feet as square yards leaves you short by a factor of nine.
• Forgetting the roll width. A room 13 ft wide on a 12 ft roll needs two strips — the second strip is mostly waste, and the calculator shows that.
• No allowance for pattern. Patterned carpet needs extra for matching. 10% is the minimum; large patterns need more.

Safety

Cutting carpet uses a sharp knife — always cut away from your body and keep fingers clear of the blade. Gripper strips have sharp pins: wear gloves when handling them. If the room has a damp floor or the old carpet smells of mould, find and fix the damp first.

Try these calculators

• Carpet Calculator — square yards, strips and linear length.
• Square Footage Calculator — room area in square feet and square metres.
• Flooring Calculator — boxes from room area and coverage per box.