Paint Calculator
Work out how many gallons of paint you need for a room, accounting for doors, windows and number of coats.
Add this calculator to your website — get the free widget
How to Calculate
Wall area = perimeter × height. Subtract about 20 ft² per door and 15 ft² per window.
One gallon covers 350–400 ft² per coat on smooth, primed walls; textured or porous surfaces need more.
Two coats are standard, especially when changing colors.
See our methodology for how every calculator on this site is built.
Worked Example: A 14 × 12 Bedroom
Walls are 9 ft high. One door, three windows, two coats, and you're doing the ceiling too. Coverage is 350 ft² per gallon.
- Perimeter: 2 × (14 + 12) = 52 ft
- Gross wall area: 52 × 9 = 468 ft²
- Openings: 1 door × 20 + 3 windows × 15 = 65 ft²
- Net wall area: 468 − 65 = 403 ft²
- Ceiling: 14 × 12 = 168 ft²
- Total for two coats: (403 + 168) × 2 = 1,142 ft²
- Paint: 1,142 ÷ 350 = 3.3 gallons
In practice the ceiling usually gets flat ceiling white and the walls get your color, so split it. Walls: 403 × 2 ÷ 350 = 2.3 gallons of wall color, so buy 2 gallons plus a quart, or 3 gallons if you want leftover for touch-ups. Ceiling: 168 × 2 ÷ 350 = 0.96 gallons. One gallon is cutting it close; a second coat on a ceiling often takes less than the first, but if it's bare drywall, buy two.
Real-World Coverage by Surface
The label number assumes smooth, primed walls and a good roller. Expect less on everything else.
| Surface | Approx. coverage per gallon |
|---|---|
| Smooth, previously painted drywall | 350–400 ft² |
| New drywall (primer coat) | 250–300 ft² |
| Orange peel or knockdown texture | 300–350 ft² |
| Popcorn ceiling | 150–250 ft² |
| Rough stucco or block | 100–200 ft² |
| Bare wood siding | 200–300 ft² |
Things That Throw Off the Estimate
Color changes
Going from a dark color to white, or putting on a deep red or navy, can take three coats unless you use a tinted primer first. A gray-tinted primer under deep colors saves a coat of the expensive stuff.
Trim is separate
Doors, baseboards and window casing usually get semi-gloss in a different color. A standard bedroom's trim takes about a quart. A room with a lot of windows and wainscoting can take a gallon.
Rollers soak up paint
A new 3/8 inch nap roller holds a good amount of paint before anything reaches the wall. On a small room that loss is noticeable. Thicker naps for texture hold even more.
Tips from the Job
- Box your paint: pour all the gallons of one color into a 5-gallon bucket and mix them. Cans from different batches can differ slightly, and you'll see it on a wall in raking light.
- Cut in one wall, then roll it while the edge is still wet. Cutting in the whole room first leaves a visible picture-frame band along the corners.
- Write the color name, brand and sheen on the lid and on the back of a switch plate. You will need it in two years.
- Keep a quart of leftover in a small sealed can rather than a mostly empty gallon. Less air means it lasts longer.
Rough Cost
Interior wall paint typically ranges from about $25 to $40 per gallon for basic lines up to $60 to $90 for premium lines. Premium paint often covers better in one or two coats, which can close the price gap on large color changes. Primer is usually $20 to $45 a gallon.
Sources
Common questions
- How much paint do I need for a 12x12 room?
- How much paint for a 10x10 bedroom, including the ceiling?
Frequently Asked Questions
How much paint for a 12×12 room?
With 8 ft walls, one door, two windows and two coats, about 1.9 gallons — buy 2.
Do I need primer?
Prime new drywall, patched areas, or when going from dark to light colors.
How much does a quart cover?
About 90 ft² — useful for trim and touch-ups.
What sheen should I use?
Flat or matte for ceilings, eggshell for living areas and bedrooms, satin or semi-gloss for kitchens, baths and trim where you need to wipe walls.
Can I skip the second coat with paint-and-primer?
Sometimes, if the new color is close to the old one and the walls are sound. Big color changes, reds and deep tones almost always need two coats.