Paint Calculator
A paint calculator works out how much paint you need by adding up your wall area, subtracting doors and windows, and dividing by the coverage of one gallon (about 350 square feet), then multiplying by the number of coats. Enter your wall dimensions below to get the gallons for one or two coats.
1 gallon ~350 sq ft per coat; subtract ~21 sq ft per door, ~15 sq ft per window; coats default 2.
- Paintable area
- 0 sq ft
- Coats
- 2
Enter your dimensions to see the gallons you need.
Estimate only. Material yields vary by product and brand; check your product label and add a margin.
How Do You Calculate How Much Paint You Need?
To calculate paint, add up the length of every wall and multiply by the wall height to get the total wall area, then subtract about 21 square feet for each door and 15 square feet for each window to get the paintable area. Divide that by 350, the square feet one gallon covers, and multiply by the number of coats. A room with 60 feet of wall at 8 feet high, one door and two windows, needs about 2.6 gallons for two coats. The calculator does this instantly.
How Much Does a Gallon of Paint Cover?
One gallon of paint covers about 350 square feet in a single coat on a smooth, primed surface. Rough, textured or porous surfaces drink up more and reduce coverage, and dark-to-light color changes often need an extra coat. Because most jobs use two coats, plan on a gallon covering roughly 175 square feet of finished wall over two coats, which is the figure the calculator uses by default.
How Many Coats of Paint Do You Need?
Two coats is the standard for a durable, even finish, and it is the calculator default. One coat may suffice when repainting the same color, while three coats can be needed for dramatic color changes or covering stains. Each coat multiplies the paint quantity directly, so set the right number of coats before ordering. Primer is calculated separately when you are covering bare or patched surfaces.
Should You Buy Extra Paint?
Yes, a little. Keeping some paint in reserve covers touch-ups, missed spots and future repairs, and matching a color later is hard once the can is gone. The calculator rounds up to whole gallons, which usually leaves a useful surplus. Buying all your paint in one batch also avoids slight color variation between batches, which matters most on large continuous walls.
Calculators in this family
How Do You Calculate Paint Needed?
Formula
Gallons = Wall Area (sq ft) / 350 x Number of Coats
- Measure the room perimeter (add the wall lengths) and multiply by the wall height for the wall area.
- Subtract the area of doors and large windows.
- Divide the wall area by 350, the square feet one gallon covers.
- Multiply by the number of coats (usually two).
Worked example
A 12 ft x 12 ft room with 8 ft walls has a 48 ft perimeter, so wall area is 48 x 8 = 384 square feet. One coat is 384 / 350 = about 1.1 gallons; two coats is about 2.2 gallons, so buy about 2.5 gallons.
- One gallon covers about 350 square feet per coat on a smooth, primed surface.
- Most jobs need two coats; deep or bright colors over light may need three.
- Primer is calculated and bought separately.
See how much paint you need (reference table by room size and coats)
Frequently asked questions
- How much paint do I need for a 12x12 room?
- A 12 by 12 foot room with 8 foot walls has about 384 square feet of wall. Minus a door and window and over two coats, it needs roughly 2 gallons of paint.
- How much does a gallon of paint cover?
- About 350 square feet per coat on a smooth primed surface. Textured or porous surfaces cover less, and most jobs use two coats, so plan on about 175 square feet of finished wall per gallon.
- How many coats of paint do I need?
- Two coats is standard for an even, durable finish. One coat can work for same-color repaints, and three may be needed for big color changes or covering stains.
- Do I subtract doors and windows when calculating paint?
- Yes. Subtract about 21 square feet per door and 15 square feet per window from your total wall area to get the paintable area before dividing by coverage.
- How do you measure a room for paint?
- Add the wall lengths for the perimeter, multiply by the wall height for wall area, then subtract the area of doors and large windows. Divide by 350 for gallons per coat.