Paint Coverage Calculator
Figure out exactly how much paint to buy — no more guessing, no wasted cans.
| Surface | Area (sq ft) | Paint (gal) |
|---|
Based on your room size and coats:
How to Use This Paint Coverage Calculator
Enter your room's width, length, and ceiling height (or add individual walls in Custom mode), then specify how many doors and windows to subtract. Choose the number of coats and your paint's coverage rate, hit Calculate, and you'll instantly see gallons needed, cost, and a full shopping list.
Why This Matters
Buying too little paint is a bigger problem than it sounds. If you run out mid-wall and have to open a second batch, even the same color code can dry slightly different — leaving a visible line that drives homeowners crazy. On the flip side, buying three extra gallons of a custom-mixed color you'll never use again wastes real money ($150+ at premium prices).
A typical 12×14 room with 9-foot ceilings has about 520 sq ft of wall surface before subtracting openings. At 350 sq ft per gallon and 2 coats, that's roughly 3 gallons. Most people buy 4 and have a half-gallon left over — that's fine. But many DIYers eyeball it and grab 2 gallons, then make an extra hardware store run on Sunday afternoon when the store is packed. This calculator eliminates that.
Contractors use roughly the same math — coverage per gallon times coats times area, adjusted for surface texture. Rough stucco or brick can cut coverage in half compared to smooth drywall.
How It's Calculated
The core formula is straightforward:
Paintable Area = (Total Wall Area) − (Door Area × Doors) − (Window Area × Windows)
Gallons Needed = (Paintable Area × Coats) ÷ Coverage per Gallon
Default assumptions: each door = 20 sq ft (standard 80"×32"), each window = 15 sq ft (standard double-hung), coverage = 350 sq ft/gal (industry standard for latex on smooth drywall). We add a 10% buffer automatically when recommending how many cans to purchase.
Tips & Common Mistakes
- Don't skip primer math. If you're painting over a dark color or bare drywall, primer is a separate product with its own coverage — usually 300 sq ft/gal. Add it to your shopping list.
- Textured surfaces need more paint. Drop coverage to 250–300 sq ft/gal for orange peel, 200 sq ft/gal for heavy knockdown or brick.
- Trim paint is separate. Doors, window frames, and baseboards use a different paint (usually semi-gloss or gloss). Budget 1 quart per room for standard trim.
- Stir, don't shake. Shaking creates bubbles. Use a mixing stick and stir for 2 full minutes. Ask the hardware store to shake it on their machine first, then re-stir before each use.
- Keep a record. Write the color code and brand on a piece of tape and stick it inside a cabinet near the room. Touch-ups 2 years later will thank you.
Frequently Asked Questions
How accurate is the 350 sq ft per gallon estimate?
It's the manufacturer's stated coverage for smooth, already-primed surfaces in ideal conditions. Real-world coverage on new drywall (more porous) or textured walls can be 15–25% lower. For safety, we recommend using 300 sq ft/gal if you're unsure about your surface.
Do I need to include the ceiling in my wall measurements?
No — the ceiling is calculated separately as its own surface (width × length). If you select "Yes" for painting the ceiling in Simple mode, it's added automatically. Ceilings typically use flat/matte paint, often a different product than your walls.
Should I buy gallons or quarts?
If you need more than 1.5 gallons, buying full gallons is almost always cheaper per ounce. A quart (0.25 gal) typically costs $15–25 at mid-range, while a gallon is $40–60 — so gallons are the better value at scale. Keep a quart of your wall color for future touch-ups.
What about second-hand or sample pots?
Sample pots (usually 8 oz or 1 pint) are great for testing a color before committing. They're not enough to paint even a small wall, but they're perfect for a 2×2 ft test patch. Let it dry fully (24 hours) and check the color in both daylight and artificial light before buying gallons.