Enter the wall area you are covering and this estimates how many gallons to buy and what it will cost — accounting for coats and the coverage on the can.
One gallon typically covers 350 to 400 sq ft per coat. Primer and dark-to-light changes may need an extra coat.
Estimating paint and its cost
Paint is sold by coverage, so cost comes down to how much wall you have and how many coats. A gallon of interior wall paint covers roughly 350–400 sq ft per coat, and most jobs need two coats. Work out paintable area — wall perimeter × height, minus about 21 sq ft per door and 15 sq ft per window — then divide by 350 and multiply by coats for gallons. Multiply gallons by your paint’s price (plus primer for bare drywall or a big color change) for the total.
Round up to whole gallons, since running short mid-wall means a store trip and a possible batch-color mismatch. A slightly larger size often costs less per gallon, and an extra quart is cheap insurance for touch-ups. Textured or porous walls drink more paint, so add a little for them.