Buy too little paint and you're back at the store mid-job; buy too much and you've wasted money. The amount you need comes down to three things: the area, the number of coats, and how far a tin of your paint actually spreads.
Most paints cover around 350 sq ft per US gallon on smooth walls — less on rough or porous surfaces. Enter your numbers and this calculator gives you the gallons and litres to buy, rounded up to whole tins.
Frequently asked questions
How much does a gallon of paint cover?
Typically 300–400 sq ft per coat on smooth surfaces. Rough, textured or unprimed walls soak up more, so coverage drops.
How many coats do I need?
Two is standard for even colour and durability. Dramatic colour changes or bare surfaces may need a primer plus two topcoats.
Should I round up?
Yes — always buy a little extra for touch-ups and to allow for uneven coverage. This tool rounds to whole tins for you.