How Much Paint Do I Need for a Room?
A typical 12 × 12 ft bedroom with 8 ft walls needs about 2 gallons of paint for two coats. Most interior wall paints cover 350 to 400 square feet per gallon per coat.
That figure moves with three things: how big the walls really are, how many coats you put on, and how much the surface soaks up. This guide works through each one so you can trust the number before you buy.
The math
Measure the length of every wall and add them up, then multiply by the height. Subtract about 20 sq ft for each door and 15 sq ft for each window. Multiply by the number of coats, divide by the coverage on the can, and add 10% for waste.
A 12 × 12 ft bedroom, 8 ft walls, one door, two windows
What changes the answer
Texture adds surface area. New drywall and bare plaster absorb the first coat, so prime them first. Going from a dark colour to a light one usually needs a third coat or a tinted primer.
What to buy
Round up to the cans sold in the store. In Canada a gallon can holds 3.78 L and a quart about 946 mL. Keep what is left, labelled with the room, for touch-ups.
Includes 10% for waste and touch-ups. Coverage changes from product to product, so check the rate printed on your can.
Questions
Is one gallon enough for a small bathroom?
Usually, for two coats on a small bathroom. Run the calculator with your sizes to check.
Should the ceiling come out of the same can?
Only if you use the same paint. Most people use flat ceiling paint, so calculate it separately.
Estimates only. The coverage printed on your paint can and the product instructions are the numbers to trust.