Interiors and flooring

What this cluster is for

Paint, flooring, carpet and worktops share the same trap. Every one of them is sold in a unit that is not the unit you measured. Paint comes in tins of set sizes, flooring in packs with a stated coverage, carpet off a fixed roll width, and worktop in stock lengths that have to be joined.

So the interesting part is not the area; it is the rounding. The paint calculator solves the tin sizes as a small coin-change problem for the least waste, the flooring calculator rounds packs up, the carpet calculator works out how many strips fit across the room and where the seams land, and the worktop calculator treats each run as a cut piece taken from a stock length.

What usually goes wrong

• Painting the floor area instead of the wall area. Litres come from wall area × coats ÷ coverage, minus doors and windows — and bare plaster drinks a first coat at a much lower coverage than the tin quotes.
• Ignoring the shape of the room when ordering flooring. Packs are computed with a waste allowance, and an L-shaped or heavily doored room needs more than a plain rectangle of the same area.
• Buying carpet on room area. Carpet is sold off a roll width — commonly 4 m or 5 m — and you pay for the full length of each strip, seams and all. A 4.2 m room off a 4 m roll means two strips and a seam.
• Measuring worktops wall to wall. A corner takes length out of the run, and a mitred corner needs an allowance on top of the measured length.
• Forgetting the trims. Underlay, gripper, door bars, scotia and beading are sold separately and scale with the perimeter, not the area.

What to order together

• Paint, primer, rollers, trays, brushes and masking tape
• Flooring packs, underlay, scotia or beading, and door bars
• Carpet, underlay, gripper rods, and door bars
• Worktop, upstand, end panels, and worktop bolts or a joining strip

Related clusters

Cross-links here are contextual, not a second home: each calculator belongs to exactly one cluster above.