Methodology
How these numbers are calculated
No black boxes. Every calculator shows its formula on the results screen, and here is the reasoning that sits behind all of them.
Everything reduces to area, volume or length
Each calculator converts your inputs into one base quantity — square metres, cubic metres or linear metres — before anything else happens. Unit switching converts the inputs, not the results, so a metric and an imperial run of the same job produce the same underlying number.
Coverage rates are editable, not hidden
Defaults come from typical manufacturer datasheets: 11 m²/L for interior emulsion, 0.11 m³ per 20 kg concrete bag, 2.4 m² per drywall sheet. Every one of these is an editable field, because the tin in your hand is the authority, not our default.
Waste is applied after the base quantity
Waste multiplies the base quantity before rounding to packs. We default to 10% and offer material-specific presets — 15% for diagonal tile layouts, 20% for herringbone flooring — because complexity drives offcuts.
Rounding always goes up to whole packages
You buy boxes, bags and cans. We round up to the nearest whole unit and report the leftover explicitly so you can decide whether to size down a pack or keep the spare for repairs.
What we deliberately exclude
We do not price labour, delivery, tool hire, permits or disposal. We do not model structural loads, span tables or code compliance. For anything structural or regulated, have a licensed professional check the plan before you buy.
Estimates are guidance, not a guarantee. Always verify quantities against product packaging and your own measurements before purchasing.