Paintable area
Calculate wall and ceiling areas separately. Deduct large openings where appropriate, but remember doors, trim and feature surfaces may require different products.
Coverage rate
Coverage printed on the tin is an estimate under stated conditions. Porous, textured or newly repaired surfaces can use more paint.
Coats and primer
Colour change, substrate condition and product system determine whether primer or additional coats are required.
Rounding
Convert the calculated volume into available container sizes. Sometimes two smaller tins reduce surplus; sometimes a larger tin is more economical.
Worked example
Regional units
BuildCalc supports the United Kingdom, United States, Canada, Australia, New Zealand, Ireland and South Africa. The geometry is universal, but terminology, units, pack sizes and common product dimensions differ. Use the dimensions printed on the product you intend to buy rather than assuming a regional default is exact.
US gallons and imperial gallons are different volumes. BuildCalc treats the selected region and unit system explicitly.
Use the related calculators
Use the calculator for your measurements, then return to this guide to check assumptions, allowances and ordering considerations.
Paint calculatorRoom paint calculator