Calculate how much paint you need for a room from its dimensions, openings, coats, and a touch-up reserve.
Usage Tip
Buy all your paint in one batch and box it together (mix the cans) so the color stays consistent across the whole room.
gallons = wall area × coats ÷ coverage × (1 + reserve)
Doors count as 21 square feet and windows as 15.
How Much Paint Do I Need?
Paint covers wall area, not floor area. Find the wall area (room perimeter times ceiling height), subtract the doors and windows, multiply by the number of coats, and divide by the coverage rate – about 350-400 sq ft per gallon for interior latex on a smooth wall.
Example: a 12 x 12 ft room with 8 ft ceilings has 384 sq ft of wall; minus a door and two windows leaves about 333 sq ft. Two coats at 375 sq ft/gal is roughly 1.8 gallons – buy 2.
Paint Coverage by Surface Type
| Paint | Coverage / gallon |
|---|---|
| Interior latex | 350-400 sq ft |
| Exterior | 300-350 sq ft |
| Primer | 200-300 sq ft |
| Ceiling paint | 350-400 sq ft |
Most major brands quote 350-400 sq ft per gallon for one coat on a primed, smooth surface; bare drywall, dark colors, and color changes effectively cut that, which is what the coats and primer options account for.
Paint Coverage by Texture
Texture increases surface area and soaks up more paint:
| Surface | Coverage adjustment |
|---|---|
| Smooth drywall | full rate (x1.0) |
| Light texture / orange peel | about 10% more (x1.1) |
| Heavy texture / knockdown / stucco | 25-40% more (x1.3) |
Spraying also uses more than rolling because of overspray – budget roughly 20-25% extra if spraying.
Coats & Primer
| Situation | Recommendation |
|---|---|
| Same color refresh | 1 coat |
| Standard repaint | 2 coats |
| Color change / dark over light | 2 coats + primer |
| Bare drywall or stains | Primer + 2 coats |
Primer covers about 200-300 sq ft per gallon. Self-priming paints can skip a separate primer on minor refreshes, but bare drywall, big color changes, and stained surfaces really do want a dedicated primer coat.
Paint Finish Guide
| Finish | Best for |
|---|---|
| Flat / matte | Ceilings, low-traffic, hides flaws |
| Eggshell | Living rooms, bedrooms |
| Satin | Kitchens, baths, kids rooms, hallways |
| Semi-gloss | Trim, doors, cabinets, high-moisture |
| Gloss | Trim and cabinets wanting a hard shine |
Room Preparation Checklist
- Move or center furniture and cover with drop cloths.
- Remove outlet and switch covers; mask anything that stays.
- Patch holes and dents; sand smooth.
- Clean walls of dust and grease; let dry.
- Tape edges, baseboards, and trim.
- Prime patches and any bare or stained spots.
Paint Drying Time Guide
| Stage | Latex / water-based |
|---|---|
| Dry to touch | about 1 hour |
| Recoat | about 4 hours |
| Fully cured | 2-4 weeks |
Oil-based paints take longer – several hours to recoat. Heat and humidity change everything; do not rush the recoat or you will pull up the first coat.
Room-Size Examples
| Room (8 ft ceiling) | Wall area | 2 coats |
|---|---|---|
| 10 x 10 | 320 sq ft | about 2 gal |
| 12 x 12 | 384 sq ft | about 2 gal |
| 12 x 16 | 448 sq ft | about 3 gal |
| 15 x 20 | 560 sq ft | about 3 gal |
Common Mistakes
- Using floor area instead of wall area.
- Forgetting the second coat when estimating.
- Ignoring texture and spraying overspray.
- Skipping primer on bare or color-changing walls.
- Buying four quarts when a cheaper gallon would do.
Frequently Asked Questions
How much paint for a 12×12 room?
About 2 gallons for two coats of wall paint, after subtracting a door and a couple of windows. Add primer for a color change.
How many square feet does a gallon of paint cover?
About 350-400 sq ft per coat on smooth, primed walls; less on texture or bare drywall.
One coat or two?
Two for most repaints. One can work for a same-color refresh; use primer plus two for big color changes or bare drywall.
Should I buy gallons or quarts?
Gallons are cheaper per volume, so round up to a gallon when you need most of one; use quarts only for small leftovers or trim. The calculator suggests the cheaper mix.
Do textured walls need more paint?
Yes – about 10% more for light texture and 25-40% more for heavy texture or stucco.
How long between coats?
About 4 hours for latex, longer for oil-based or in cool, humid conditions.
Related Calculators
Note: coverage and cost figures are approximations. Actual coverage varies with paint brand, color, surface texture and porosity, application method, and number of coats – always check the can label and buy a little extra for touch-ups. General DIY guidance, not a professional estimate.