Last updated: May 2026
Enter your room dimensions and get exact gallons needed — walls, ceiling, coats, and all.
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Paint Settings
Premium paints often cover 400 sq ft/gal; cheaper paints 250–300 sq ft/gal.
Results
Paint Coverage by Finish Type
| Finish | Coverage (sq ft/gal) | Best for |
|---|---|---|
| Flat / Matte | 400 | Ceilings, low-traffic rooms |
| Eggshell | 350 | Living rooms, bedrooms |
| Satin | 325 | Hallways, kids' rooms |
| Semi-Gloss | 300 | Kitchens, bathrooms, trim |
| Gloss / High-Gloss | 275 | Cabinets, doors, accents |
| Primer | 200 | New drywall, dark coverage |
Wall area: Perimeter × Ceiling height − (doors × 20) − (windows × 15). Perimeter = 2 × (Length + Width).
Ceiling area: Length × Width (included only if "Include ceiling" is checked).
Trim/baseboards: When checked, adds 10% to the wall area to account for extra edges and cut-in work.
Total paintable area: Wall area + Ceiling area (if included).
Gallons needed: (Total paintable area × Number of coats) ÷ Coverage rate per gallon. Always round up to the nearest quart (0.25 gal).
Cost estimate: Gallons (rounded up) × Price per gallon entered.
Standard interior paint covers 350–400 square feet per gallon with one coat. That's the manufacturer's ideal number — on fresh drywall with a roller on a smooth surface. Real-world coverage is typically 300–350 sq ft per gallon, especially on textured walls, new drywall (which absorbs more), or when rolling over a dramatically different color.
Two coats are almost always recommended. One coat over white or similar-tone paint is sometimes fine for touch-ups and minor color changes, but a true color change — especially light-over-dark — usually requires two coats minimum, and occasionally three. Always buy enough for two coats upfront; matching paint from a second can is never guaranteed to be identical.
| Finish | Sheen Level | Best For | Cleanability |
|---|---|---|---|
| Flat / Matte | None | Ceilings, low-traffic walls | Poor — marks easily |
| Eggshell | Low | Living rooms, bedrooms | Moderate |
| Satin | Medium-low | Hallways, kids' rooms, family rooms | Good |
| Semi-gloss | Medium-high | Kitchens, bathrooms, trim | Very good |
| Gloss | High | Trim, doors, cabinets | Excellent |
How many gallons of paint do I need for a 12x12 room?
A 12×12 room with 8-ft ceilings, two doors, and two windows requires about 280 sq ft of paintable wall area. At 350 sq ft per gallon, that's about 0.8 gallons per coat. For two coats: 1.6 gallons — buy 2 gallons. If you're also painting the ceiling (144 sq ft), add another half-gallon, so 2.5 gallons total.
What's the difference between primer and paint?
Primer seals the surface, improves adhesion, and blocks stains or tannins from bleeding through. Paint provides the color and finish. Modern "paint + primer" formulas do both adequately for repaints over similar colors, but a separate primer coat is worth it when painting new drywall (which needs sealing), covering dark colors, or painting over stained or water-damaged surfaces.
How long does it take paint to dry between coats?
Latex (water-based) paint is typically touch-dry in 1–2 hours and ready for a second coat in 4 hours. Oil-based paint takes 6–8 hours to recoat. "Dry" and "cured" are different — paint reaches full hardness and washability in 2–4 weeks for latex, longer for oil. Avoid scrubbing or heavy cleaning during that curing window.
Can I use leftover exterior paint inside?
Not recommended. Exterior paint contains mildewcides, UV stabilizers, and other additives that can off-gas indoors. Interior paint is formulated for enclosed air quality standards. The reverse is also true — interior paint won't hold up to outdoor weather. Always use paint rated for its intended environment.
How much should I add for waste and touch-ups?
Buy 10–15% extra beyond your calculated amount. This covers: roller waste (paint absorbed by the roller nap that doesn't reach the wall), cut-in edges, inevitable spills, and future touch-ups. Touch-up paint from the same batch stored properly can last years — label the can with the room name, paint brand, color name, and finish for easy reference.