The formula is simple. The mistakes are common. Here is how to get it right the first time.
Buying too little paint means a second trip to the store and a potentially unmatched tint. Buying too much wastes money and leaves you with cans to dispose of. The right amount comes from a simple formula most people never bother to calculate.
Example: A 12×14 ft room with 9 ft ceilings, 2 doors, and 2 windows:
Perimeter = (12+14+12+14) = 52 ft × 9 ft = 468 sq ft
Subtract: 468 − (2×21) − (2×15) = 468 − 42 − 30 = 396 sq ft
Gallons needed: 396 ÷ 350 = 1.13 gallons per coat
Two coats: 2.26 gallons → buy 3 gallons
Enter your room dimensions and our calculator gives you the exact gallon count for any number of coats.
Paint Calculator →| Paint Type | Coverage per Gallon | Notes |
|---|---|---|
| Standard wall paint | 350–400 sq ft | Smooth surfaces, one coat |
| Primer | 200–300 sq ft | Porous or unpainted surfaces |
| Ceiling paint | 350–450 sq ft | Thicker formula, more coverage |
| Textured paint | 150–200 sq ft | Adds texture, lower coverage |
| High-gloss trim paint | 300–350 sq ft | Denser, less spread |
Primer is required when painting over bare drywall, a dark color with a lighter one, a damaged or patched wall, or a glossy surface. Skip primer on surfaces that are already painted with a similar color and in good condition. Most modern paints labeled "paint and primer in one" still benefit from a separate primer coat on bare surfaces — the label is marketing, not physics.