Carpet Calculator

Multiply length by width, subtract any areas not carpeted, and add a waste allowance. Then divide by the coverage per roll and round up — you cannot buy part of a roll.

Because it comes in fixed widths, commonly 4 m or 5 m. A room 4.2 m wide needs a 5 m roll and wastes 0.8 m down its entire length, whatever the area calculation says.

Ten percent for a plain rectangular room, more for an awkward shape and more again for a patterned carpet that needs matching across seams.

Considerably. Carpet looks different depending on which way the pile runs, so all pieces in a room must be laid the same way — which constrains how offcuts can be used and increases waste.

Underlay is the same area and comes in different roll widths, so it needs its own calculation. It also has less pile-direction constraint, so waste is usually lower.

Yes — carpet normally runs to the centre of the door opening where it meets another floor covering. Measuring to the wall leaves a strip short at every doorway.

Break it into rectangles, measure each and add them. Measure at the widest point of each rectangle, since carpet cannot be stretched to fill a gap.

Fitted carpet is stretched over gripper rods and held under tension, which keeps it flat for years. Loose lay sits on the floor and moves, and it is only suitable for small areas or temporary use.

It needs a small excess for trimming rather than expansion — usually 50 to 100 mm all round. Cutting exactly to size leaves nothing to work with when the room turns out not to be square.

It varies enormously with fibre, pile density and traffic. Density matters more than pile height — a dense short pile outlasts a deep sparse one in a hallway by a wide margin.

It should match the traffic rather than the carpet. Too soft an underlay under a heavy-traffic carpet lets the backing flex and fail early, which shortens the carpet's life rather than extending it.

Over a sound, flat, dry subfloor, generally yes. Over old carpet, no — the layers move independently and the top one wears through at every seam and edge.