ProjectFigure Exact material estimates for every home & DIY project.

Paint Calculator

A paint calculator works out how many gallons you need for a room, based on the wall area and how many coats. Enter your measurements and it sizes the paint, so you buy enough to finish without a mid-job run to the store - or a shelf of leftover cans.

Your measurements

Result

Paint is heavy and ships poorly, so most people buy it locally - but the supplies that make the job painless (a good roller kit, drop cloths, painter's tape) ship to your door, and that is what the shopping list focuses on.

How it is calculated

Paint needed = wall area times coats, divided by the spread rate (about 350 sq ft per gallon for interior wall paint), rounded up to whole gallons. Primer, deep colours and rough or porous surfaces lower the spread rate and may need an extra coat.

Steps

Choose to measure by room perimeter and height, or total wall area.
Enter the measurements in feet (or metres).
Set the number of coats - two is standard for a colour change.
Read the gallons to buy, rounded up to whole cans.
Grab the roller kit, drop cloths and tape so you are not improvising.

Worked example

A room with a 40 ft perimeter and 9 ft walls is 360 sq ft. At two coats and ~350 sq ft per gallon, that is 2.1 gallons - round up to 3 one-gallon cans.

Common questions

How much paint do I need for a room?

Wall area times coats divided by ~350 sq ft per gallon. A typical bedroom takes 2-3 gallons for two coats.

How many coats?

Two for most colour changes. One can do if you are refreshing the same colour; three if you are going light over dark.

Should I subtract doors and windows?

For one or two, it roughly cancels out with the spare you should keep for touch-ups. For lots of glazing, deduct the area.

Why does the shopping list skip the paint itself?

Paint is heavy and usually cheaper locally. The rollers, trays, drop cloths and tape are what ship well and make the job easier.