How to calculate how much paint you need
Work out the area you're painting, take away the doors and windows, multiply by the number of coats, and divide by how far one gallon goes. The coverage figure is printed on every can.
Wall area = 2 × (length + width) × height − doors − windows
Gallons = area × coats ÷ coverage per gallon
Example: a 12 × 12 ft room with 8 ft walls has 384 sq ft of wall. Take away one door (21 sq ft) and one window (15 sq ft) and you have 348 sq ft. Two coats is 696 sq ft of painting, which at 350 sq ft per gallon is 1.99 gallons. Buy 2 gallons.
Paint coverage by surface
| Surface | Approx. coverage per gallon |
|---|---|
| Smooth, previously painted drywall | 350–400 sq ft |
| New drywall (after primer) | 300–350 sq ft |
| Textured walls or ceilings | 250–300 sq ft |
| Rough wood, stucco or masonry | 200–250 sq ft |
Buying the right amount
- Round up to the container size. If you need 2.2 gallons, buy 2 gallons and a quart rather than 3 gallons.
- Four gallons or more? A 5 gallon bucket is usually cheaper per gallon and keeps the color consistent.
- Keep a little extra for touch-ups, and write the brand, color name and sheen on the lid.
- Trim and doors are usually done in a different sheen. One quart covers the trim in a typical bedroom.
Frequently asked questions
How much area does a gallon of paint cover?
Most interior paint labels say one gallon covers about 350 to 400 square feet per coat on smooth, primed walls. Textured, porous or unprimed surfaces soak up more, so expect closer to 250 to 300 square feet per gallon there.
How much paint do I need for a 12x12 room?
A 12 × 12 room with 8 foot walls has 384 square feet of wall. After subtracting a door and a window, two coats at 350 square feet per gallon need about 2 gallons. Add roughly 1 more gallon for two coats on the ceiling.
Do I need two coats of paint?
Usually, yes. Two coats give even color and better durability, especially when changing colors. One coat can be enough when repainting the same color over a clean wall, or with some paint-and-primer products on a light change.
Should I use primer?
Use primer on new drywall, patched areas, stained walls, glossy surfaces, and when making a big color change such as dark to light. Primer seals the surface so your topcoat covers evenly and you use less of it.
Is it cheaper to buy a 5 gallon bucket?
Often, if you need four gallons or more of the same color. A 5 gallon bucket usually costs less per gallon and keeps the color consistent across a large job. For smaller amounts, gallons plus a quart for touch-ups works well.