Paint Coverage Calculator
Calculate how many gallons of paint you need from wall area, number of coats, doors and windows to subtract, and paint coverage rate.
How to use this tool
- Measure each wall (length x ceiling height) and add the areas together.
- Estimate the area of doors and windows you won't paint and enter that to subtract.
- Choose the number of coats — two is standard.
- Enter the coverage rate from your paint can (default 350 sq ft/gal).
- Read the gallons to buy, rounded up to whole cans.
Buy the right amount of paint the first time. Enter your wall area, subtract doors and windows, choose your number of coats, and this tool tells you how many gallons to pick up.
Formula
Subtract un-painted openings from the wall area, multiply by coats, and divide by the spread rate:
Net area = Wall area − Doors & windows
Gallons = ⌈ (Net area × Coats) ÷ Coverage per gallon ⌉
The result is rounded up because paint is sold in whole cans. A typical gallon of interior latex covers about 350 sq ft per coat on smooth, primed drywall.
How it works
Estimating paint starts with the net surface area: total wall area minus the doors, windows, and other openings you will not paint. We multiply that by the number of coats, then divide by the paint's spread rate to get the volume required. The default 350 sq ft per gallon reflects a smooth, primed interior wall painted with quality latex; rough, porous, or unprimed surfaces drink more paint and can drop coverage to 250 sq ft or less.
We round the final figure up to whole gallons because retailers sell paint in whole or quart cans, and running out mid-wall risks visible lap marks from a fresh batch with a slightly different tint. Buying one container per color also leaves a small reserve for touch-ups, which we treat as a built-in cushion rather than a separate waste factor.
For a major color change — covering dark walls with a light color, or vice versa — plan on a primer coat plus two finish coats and enter three coats. Texture, spray application, and dark accent colors all increase consumption, so check the spread rate printed on your specific can and adjust the coverage field accordingly.
Worked example
600 sq ft of wall, 2 coats, one door and three windows
- Net area = 600 − 60 = 540 sq ft.
- Total coverage needed = 540 × 2 coats = 1,080 sq ft.
- Exact gallons = 1,080 ÷ 350 = 3.09 gal.
- Round up to whole cans: ⌈3.09⌉ = 4 gallons.
Buy 4 gallons | Exact 3.09 gal | Net area 540.00 sq ft
Gallons needed by wall area and coats (350 sq ft/gal)
| Net wall area | 1 coat | 2 coats | 3 coats |
|---|---|---|---|
| 200 sq ft | 1 gal | 2 gal | 2 gal |
| 400 sq ft | 2 gal | 3 gal | 4 gal |
| 600 sq ft | 2 gal | 4 gal | 6 gal |
| 800 sq ft | 3 gal | 5 gal | 7 gal |
| 1,200 sq ft | 4 gal | 7 gal | 11 gal |
Key terms
- Coverage (spread rate)
- The area one gallon of paint covers in a single coat, printed on the can. Interior latex is typically 350-400 sq ft/gal on smooth surfaces.
- Coat
- One complete application of paint over the surface. Two coats are standard for an even, durable finish.
- Primer
- A preparatory coat that seals the surface and improves adhesion and uniformity of the finish coats. It counts as an extra coat when estimating.
- Net paintable area
- Total wall area minus the area of doors, windows, and other openings that will not be painted.
Frequently asked questions
- How many gallons of paint do I need for a room?
- Add up the wall area, subtract doors and windows, multiply by coats, then divide by about 350 sq ft per gallon. A typical 12x12 room with 8 ft ceilings needs roughly 2 gallons for two coats.
- How much does one gallon of paint cover?
- About 350-400 sq ft per coat on smooth, primed drywall. Rough, textured, or unprimed surfaces can drop that to 250 sq ft or less, so check the spread rate on your can.
- Do I need primer, and does it count as a coat?
- Use primer over bare drywall, stains, or a big color change. Yes — count primer as an additional coat when estimating, since it consumes paint at a similar rate.