Building materials calculators

Getting quantities right

Each calculator gives the amount in the units merchants sell: bags, tonnes, bulk bags, boxes, panels and lengths. You can type measurements in metres or in feet and inches straight off the tape.

Every one adds an allowance for waste, and you can change it. Five per cent is about right for simple, square jobs. Go up to ten or fifteen per cent for curves, diagonal layouts, rough ground or if it’s your first go.

Ordering tips

• Check what a bulk bag weighs before you order. Bag sizes vary between merchants, from about 600kg to over a tonne.
• Ask whether delivery is kerbside or by crane, and whether there’s room to drop a bag where you need it.
• Buy bricks, tiles and blocks for the whole job in one order so the colour batch matches.
• Structural work, like footings for an extension or a retaining wall, needs a design from an engineer and usually building control approval. These calculators are for ordering, not design.

Figures last checked 25 October 2026.