Paint Calculator
Calculate how much paint and primer you need for walls, ceilings, or trim. Enter room dimensions and coats to get gallons for your project.
Last updated 2026-08-21
What Is a Paint Calculator?
The paint calculator estimates how many gallons of paint and primer you need for a painting project. You enter your total wall area, the number of coats, and the coverage rate of your paint, and it returns the exact gallons to buy. It is built for homeowners and DIYers who want to avoid running short mid-project or overspending on leftover cans.
How It Works
Gallons = ceil((Wall area × Coats) ÷ Coverage per gallon). Default coverage: 350 sq ft/gal.
Example
For 1,400 sq ft and 2 coats at 350 sq ft/gal: (1400 × 2) ÷ 350 = 8 gallons.
How to Calculate
- Measure the total area you plan to paint. For a rectangular room, add up each wall (length × height) and include any trim, accent walls, or wainscoting you want covered.
- Enter the wall area in square feet into the Wall Area field. For example, a room with 1,400 sq ft of paintable wall.
- Set the Number of Coats. Two coats is standard for most walls. With 1,400 sq ft and 2 coats, you need 2,800 sq ft of coverage total.
- Leave the coverage per gallon at the default of 350 sq ft per gallon, or enter the rate printed on your paint can. Divide total coverage by the rate: 2,800 ÷ 350 = 8 gallons.
- Round up to the nearest full gallon when buying. A gallon is the smallest size that covers a full coat on most projects, so buy 8 gallons and plan one extra can only if your walls are very porous.
How much paint one gallon covers
| Surface | Coverage per gallon |
|---|---|
| Smooth interior wall | 350 to 400 sq ft |
| Textured or stucco wall | 200 to 250 sq ft |
| Unprimed drywall | 250 to 300 sq ft |
| Primed drywall | 350 to 400 sq ft |
| Cedar or rough wood | 250 to 300 sq ft |
| Previously painted wall | 350 to 400 sq ft |
Sources
Frequently Asked Questions
How much area does a gallon cover?
One gallon covers about 300–400 sq ft with a single coat, depending on surface texture and sheen.
Do I count every coat?
Yes — multiply the area by the number of coats. Primer counts separately.
Why leave coverage blank?
If you leave it empty, the calculator assumes 350 sq ft per gallon, a standard default.
Estimate the cost with the Paint Cost Calculator. Also try: Wall Paint Calculator, Ceiling Paint Calculator or browse Paint Calculators