Running short mid-job means a second trip to the merchant; over-ordering wastes money. These four calculators give you a sensible estimate before you buy. All figures are metric (metres, millimetres, litres, cubic metres, tonnes), and everything runs in your browser — nothing you type is sent anywhere. Order results are estimates: always add a margin for waste, which the notes below explain.
How much paint do I need?
Enter the surface size and number of coats. Typical emulsion covers about 11 m² per litre, per coat — adjust if your tin states otherwise.
Concrete for a slab or footing
Enter the footprint and thickness. Bag count is for dry ready-mix at the chosen bag size — order around 10% extra.
Gravel, sand or sub-base
Enter the area and depth, then pick the material. Loose aggregate compacts, so order a little extra for anything that gets rolled or tamped.
Boards to cover an area
For decking, flooring or cladding. Enter the area and your board size — the gap is the spacing left between boards (use 0 for tongue-and-groove).
Always order a margin for waste
No job uses material with zero loss. Boards get cut to length and the offcuts are often too short to reuse; tiles and boards break; paint soaks unevenly into a porous first coat; and loose aggregate settles once it's compacted. As a rule of thumb, add 5–10% for paint, 10% for boards, tiles and cladding, and a little extra concrete and sub-base for anything that gets tamped or rolled. The timber calculator above already lets you build in a waste percentage; for the others, round up and keep a bit in reserve.
Why coverage and density are only estimates
Paint coverage depends heavily on the surface: bare plaster and timber drink the first coat, so real-world coverage on a fresh wall is often below the tin's headline figure. Aggregate density shifts with moisture and grade — a tonne of wet sand occupies less space than the dry figure suggests. And bagged concrete yield varies a little between brands. The numbers here use sensible industry averages, which are right for ordering purposes, but treat the bag's own stated coverage or your supplier's figures as the final word.
Buying concrete: bags vs. ready-mix
Below roughly half a cubic metre, bagged dry mix is usually the practical choice. Past that, ordering ready-mixed concrete delivered by volume is cheaper and far less work than mixing dozens of bags by hand. The cubic-metre figure above is what a ready-mix supplier will want; the bag count is there for smaller pours.
Do these numbers include waste already?
Why is concrete sold by volume but bags by weight?
My sub-base needs compacting — should I order more?
This calculator is provided for general planning convenience. It gives approximate quantities based on standard coverage rates and material densities; it is not a substitute for professional measurement or your supplier's figures. For structural, electrical or gas work, consult a qualified professional. Always confirm quantities before ordering.