Estimate how much paint you need for a room. Enter the room size, doors and windows, and the number of coats, and the calculator tells you how many gallons and quarts to buy.
Last updated: October 2, 2026
Estimates assume smooth, previously painted walls. Textured, porous or dark surfaces need more paint.
How the estimate works
wall area = 2 × (length + width) × height − doors × 20 − windows × 15
gallons = (wall area + ceiling area) × coats ÷ coverage per gallonMost interior paints cover roughly 350 to 400 square feet per gallon on smooth, primed walls. The exact figure is printed on the can, so enter it for a more precise result. When the leftover is three quarts or more, the calculator rounds up to a full gallon, since a gallon usually costs about the same as three quarts.
When you’ll need more paint
- New drywall or bare wood: prime first; unprimed surfaces soak up paint.
- Big color changes: going from dark to light usually takes an extra coat, or a tinted primer.
- Textured walls: texture increases the real surface area.
- Touch-ups: keep a little extra from the same batch for future repairs.
Frequently asked questions
How many coats of paint do I need?
Two coats is the norm for an even, durable finish. One coat can be enough when repainting the same color with a quality paint.
Should I include trim and doors?
Trim and doors are usually painted with a different finish, such as semi-gloss. Estimate them separately; a quart often covers the trim of a standard room.