Home & DIY Calculators

Estimating materials for a job

Almost every material estimate is the same three steps. Work out an area or a volume, add something for waste and offcuts, then divide by what a bag, box, or bundle actually holds — and round up, because you cannot buy four fifths of a bag of concrete. These tools do all three, and show the intermediate numbers so you can check them against a merchant's quote.

The concrete calculator handles slabs, strip footings, and round post holes, and converts the volume into bags at the yield printed on them. Thepaint calculator takes a room's dimensions and deducts the doors and windows before applying the spread rate. Thetile calculator accounts for the grout gap and the extra waste a diagonal or herringbone layout creates, and themulch, soil and gravel calculatorconverts a bed's area and depth into cubic yards, bags, or tons.

Two of these deserve particular attention because they are where estimates most often come up short. A pitched roof is considerably larger than the building underneath it — between 5% and 40% larger depending on the pitch — so the roofing calculator applies that pitch factor before working out squares and bundles. And a fence run always needs one more post than it has sections, which thefence calculator gets right along with the concrete for the holes.

Every tool here takes imperial or metric measurements and reports both, since materials are quoted in cubic yards in some places and cubic metres in others. Treat the results as a shopping list rather than a specification: bag yields and coverage rates vary between manufacturers, so check the figures on the product you are actually buying.