How we calculate: flooring

Flooring calculator

Open the flooring calculator

1. Floor needed (m²) = area × (1 + waste)
2. Packs = floor needed ÷ coverage per pack, rounded up; left over = packs × coverage − floor needed
3. Underlay rolls = area × (1 + waste) ÷ coverage per roll, rounded up
4. Trims = (perimeter − doorways) × (1 + waste) ÷ trim length, rounded up

Order a sample first: colour and finish vary between screens and batches.

Self-levelling compound calculator

Open the self-levelling compound calculator

1. Average depth = (thinnest + thickest) ÷ 2 for a tapered pour
2. Compound (kg) = area (m²) × average depth (mm) × consumption (kg/m²/mm) × (1 + waste)
3. Bags = kg ÷ bag size, rounded up; primer (L) = area ÷ primer coverage; water = bags × water per bag

Consumption, maximum depth and mixing water vary by product: use the figures on your bag.

This calculator has no built-in defaults: every figure comes from you or your product's data.

Carpet calculator

Open the carpet calculator

1. Rooms: strips of the roll width run one way (the pile must run the same way on every piece); enough strips to cover the other way; each strip is cut to the room length + trim
2. Carpet bought = strip widths × cut length; the direction that buys least wins unless you fix the pile direction
3. Seams = strips − 1; gripper = room perimeter − doorways; underlay rolls = floor area ÷ roll size, rounded up
4. Stairs: runner length = treads × (tread depth + nosing wrap) + risers × riser height + trim, cut from the narrowest roll that covers the width

Carpet is sold off the roll by the linear metre at the roll width, so a room slightly wider than 4 m often needs a 5 m roll or a seam.

Fitters usually add a little length to trim in at each wall; add it under More settings.

Loft boarding calculator

Open the loft boarding calculator

1. Boards = length × width × (1 + waste) ÷ (board length × board width), rounded up; packs = boards ÷ boards per pack, rounded up
2. Boards run across the joists, so each row of boards (one board width) crosses every joist once
3. Joist lines = width across the joists ÷ joist centres, rounded up, + 1; board rows = length along the joists ÷ board width, rounded up
4. Legs = joist lines × board rows (one leg at each crossing); screws = legs × screws per leg + boards × screws per board

Squashing loft insulation reduces how well it works, so the legs should lift the boards clear of it.

Ceiling joists aren't always designed to carry storage loads: if in doubt, ask a builder or structural engineer.