Home & DIY
Paint Calculator
Find out how many gallons of paint you need for a room, based on its size, openings, and number of coats.
How this is calculated
This calculator adds up the area of all four walls (perimeter × height), then subtracts the area of your doors and windows to get the actual paintable surface. It multiplies that by your number of coats, then divides by how much area one gallon covers, to tell you exactly how much paint to buy.
The "suggested to buy" amount rounds up to the nearest quarter gallon so you don't come up short mid-project, since most stores sell paint in gallon and quart sizes.
Frequently asked questions
How much paint do I need for a 12x12 room?
For a 12x12 room with 8-foot ceilings and two coats, you'll typically need about 2 gallons after subtracting a standard door and two windows. Exact amounts vary with your specific openings and paint's coverage rate.
How much wall area does one gallon of paint cover?
Most standard interior paint covers about 350–400 square feet per gallon in a single coat. Textured or unprimed walls may need more.
Do I need to paint two coats?
Two coats is standard for most color changes and gives the most even, durable finish. One coat can work for touch-ups or a very similar replacement color.
Should I buy extra paint?
It's wise to round up to the nearest full gallon and keep a little extra for touch-ups later, since paint batches can vary slightly in color between purchases.