How Much Paint Do I Need? A Simple Guide That Saves You Money

Published 2026 ? 4 min read

Buying too little paint means a second trip and a risk of mismatched color. Buying too much means wasted money. The right amount is easy to estimate ? you just need your room's wall area and a realistic coverage figure.

The quick method

Measure the length and width of the room, then add them together and double it for the perimeter. Multiply by the wall height to get the wall area. Subtract doors and windows, multiply by the number of coats you plan, and divide by about 350 square feet per gallon. That's your answer in gallons.

Why a second coat matters

One coat rarely covers properly ? darker paint over lighter walls almost always needs two. Always calculate for the coats you'll actually apply, not the minimum you hope to get away with.

Don't forget the extras

• Primer on bare drywall, stains or drastic color changes.
• Trim and doors ? a different finish usually means separate paint.
• Crown molding and ceilings if you're painting them.

Round up to the nearest gallon

Paint is sold in gallons, so always round up. It's cheaper to have half a gallon left over than to chase the exact dye-lot match later.

Run the numbers

Use the paint calculator ? enter your room size, wall height, and coats, and it tells you the wall area and gallons needed in seconds.