How Much Paint Do I Need? A Simple Room-by-Room Guide

Buy too little paint and you're making a mid-project run to the store (and risking a colour that doesn't quite match). Buy too much and you've wasted money. Here's how to estimate what you need so you buy the right amount once.

The rule of thumb

One gallon of quality interior paint covers roughly 350–400 square feet in a single coat. Most jobs need two coats, so a good working number is about one gallon per 175–200 square feet of wall for a proper two-coat finish. Porous, rough, or dramatically different colours will pull that number down.

How to measure your room

It's simple math: measure the length of each wall, add them together to get the room's perimeter, then multiply by the wall height. That's your total wall area. For a standard room you can paint right over the door and window openings in your estimate — the small overage gives you a helpful cushion for touch-ups. Example: a 12×14 room with 9-foot ceilings has a perimeter of 52 feet × 9 = about 468 square feet, so roughly 2–3 gallons for two coats.

Don't forget these

• Coats: plan on two. Deep colours, big colour changes, and bright whites over patchy walls can need a third — or a tinted primer to save coats.
• Ceilings: length × width for the area; ceilings often take their own flat paint.
• Trim and doors: usually a quart or two covers the trim in an average room; a single door takes surprisingly little.

When a 5-gallon pail makes sense

If your estimate is more than about four gallons of the same colour — a whole main floor, a large space, or a big exterior — buy the pail. You'll get consistent colour across the whole job and save $25 versus buying the gallons separately (more in our post on everyday pail savings).

Let us do the math with you

Not a fan of the arithmetic? Bring or text us your room dimensions at (403) 270-9696 and we'll calculate exactly what you need — and make sure you leave with the right amount plus a little extra for touch-ups. Visit us at 321 19 St NW or get in touch.