Build calculators

Most material questions come down to one of three measurements. Area (length × width) drives tiles, flooring, paint, plasterboard, insulation and patio slabs. Volume (area × depth) drives concrete and screed. Count tools such as the brick and block calculators turn a wall area into units using the size of each unit plus its mortar joint.

Waste allowances

Area, volume and face-area counts follow the dimensions entered: for example, concrete volume is slab area × depth, while tile count starts from floor area ÷ tile face area. These geometric quantities do not predict usable material after cuts, breakages, openings or a particular laying pattern. Waste fields are editable planning allowances, not universal rates; choose one for the job and check supplier or installer guidance.

Use the manufacturer's figures when you have them

Paint coverage, insulation coverage per roll, concrete yield per bag and flooring pack coverage depend on the product and its instructions. Defaults are illustrative and editable, not guaranteed yields. Enter the coverage or yield stated on the chosen packaging or manufacturer data. Likewise, brick and block counts use assumed unit dimensions and mortar joints; confirm these against the specified product and bond before ordering.

Metric and imperial

Measure consistently and check which unit each field expects before entering a value — a depth in millimetres entered into a metres field gives an answer a thousand times too large. The concrete volume calculator lets you switch its length fields between metres and feet.

For concrete work, start with the concrete volume calculator, then use the concrete bag calculator to turn that volume into bags to buy.