Paint Calculator
Calculate exactly how many gallons of paint you need for walls, ceilings, and trim. Enter room dimensions and get paint quantity by coat, sheen type, and surface condition.
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sq ft/gal
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Enter your values above to see the results.
Tips & Notes
- ✓Calculate ceiling area separately from walls — ceilings typically use flat finish while walls use eggshell or satin, and you may be using different products for each surface.
- ✓Buy an extra quart of the final wall color and store it with the room name and paint code written on the lid — touch-ups a year later require the exact same formula batch, which stores cannot always reproduce.
- ✓Apply primer before painting new drywall or drastic color changes — skipping primer on new drywall requires 3+ coats of finish paint to achieve coverage equivalent to 1 primer coat plus 2 finish coats.
- ✓Stir paint thoroughly before use and between coats — pigment settles during storage, and a poorly stirred can produces streaked results even with quality paint.
- ✓For large rooms, buy all paint for the project from the same store visit and the same batch lot — color consistency between cans from different production runs can be visible on large surfaces in certain lighting conditions.
Common Mistakes
- ✗Not subtracting windows and doors from wall area — a room with two large windows and a door can have 50–80 sq ft of openings, reducing paint needed by 10–15% of a standard room.
- ✗Assuming one coat of paint covers adequately — professional painters standard is two coats on previously painted walls and three coats when making a drastic color change.
- ✗Using the same coverage rate for textured and smooth walls — orange peel or knockdown textures have more actual surface area than their flat measurement suggests, requiring 15–20% more paint.
- ✗Buying paint without accounting for primer on bare surfaces — new drywall, bare wood, and patched areas require primer before topcoat, which is calculated and purchased separately.
- ✗Painting in cold temperatures — most latex paints require temperatures above 50°F for proper film formation. Painting below this threshold produces a finish that peels within months.
Paint Calculator Overview
Paint quantity estimation is deceptively straightforward — yet most homeowners either buy 30% too much or run short mid-wall and face the near-impossible task of color-matching a second can from the same formula. Accurate calculation requires measuring paintable surface area, knowing your paint coverage rate, accounting for the number of coats, and subtracting doors and windows — all before you visit the store.
Paint quantity formula:
Gallons Needed = (Total Paintable Area ÷ Coverage per Gallon) × Number of Coats
EX: Room 12 ft × 14 ft, 9 ft ceilings, 2 windows (15 sq ft each), 1 door (20 sq ft) → Wall area = 2(12+14) × 9 = 468 sq ft − 50 sq ft openings = 418 sq ft paintable → At 350 sq ft/gal: 418 ÷ 350 = 1.19 gal → 2 coats = 2.38 gal → Buy 3 quarts (2.4 gal total)Paint coverage rates by type and surface condition:
| Paint Type | Coverage (sq ft/gal) | Coats Needed | Best Use |
|---|---|---|---|
| Flat / Matte | 350–400 | 2 | Ceilings, low-traffic walls |
| Eggshell | 350–400 | 2 | Living rooms, bedrooms |
| Satin | 300–350 | 2 | Kitchens, bathrooms, hallways |
| Semi-gloss | 300–350 | 2 | Trim, doors, cabinets |
| Gloss | 250–300 | 2–3 | High-wear surfaces, furniture |
| Primer (drywall) | 200–300 | 1 | New drywall, stain blocking |
| Exterior latex | 300–400 | 2 | Siding, exterior wood |
| Condition | Adjustment | Reason |
|---|---|---|
| New drywall (unpainted) | +25–30% | Highly absorptive surface, primer essential |
| Covering dark with light color | +50–100% (extra coat) | May need 3 coats for full coverage |
| Textured walls (orange peel) | +15–20% | Surface area greater than flat measurement |
| Sprayer application | +20–30% | Overspray loss and higher film build |
| Brush/roller (standard) | +5–10% | Tray waste and edge cleanup |
| Previously painted, same color | +0% | One coat touch-up may suffice |
Frequently Asked Questions
Wall area: perimeter = 2(12+14) = 52 ft × 8 ft = 416 sq ft. Subtract an average door (20 sq ft) and two windows (15 sq ft each): 416 − 50 = 366 sq ft paintable area. At 350 sq ft/gallon: 366 ÷ 350 = 1.05 gallons per coat. For 2 coats: 2.1 gallons. Buy 1 gallon + 1 quart (totaling 1.25 gallons) and if the coverage rate is closer to 400 sq ft/gal, one gallon may cover both coats with careful application.
Sheen refers to how much light the dried paint reflects. Flat/matte has no sheen — it hides imperfections best but cannot be scrubbed. Eggshell has a slight sheen and handles light cleaning — the standard for bedrooms and living rooms. Satin is moderately shiny and cleanable — ideal for kitchens and hallways. Semi-gloss is noticeably shiny and highly washable — the standard for trim, doors, and bathrooms. Gloss is very shiny and the most durable — used for cabinets and furniture.
Yes in three situations: painting new drywall (primer is essential — drywall paper absorbs paint unevenly), making a drastic color change (dark to light or vice versa — primer reduces the number of topcoats needed), and painting over stains or repaired patches (stain-blocking primer prevents bleed-through). For normal repaints in similar colors on previously painted walls in good condition, primer is optional but improves adhesion and coverage uniformity.
Latex (water-based) paint: dry to the touch in 1 hour, recoat after 2–4 hours, fully cured in 30 days. Oil-based paint: dry to touch in 6–8 hours, recoat after 24 hours, fully cured in 3–7 days. Cure means the paint has reached its full hardness and washability — avoid scrubbing freshly painted surfaces before the cure period. Interior paint cure times depend on temperature and humidity; cool, humid conditions slow curing significantly.
Most quality interior latex paints cover 350–400 sq ft per gallon on a smooth, previously painted surface with one coat. Coverage drops to 200–300 sq ft per gallon on new drywall, textured surfaces, or very porous materials. Exterior paints typically cover 300–400 sq ft per gallon on smooth siding but less on rough or weathered wood. Always check the specific coverage rate on the paint label — it varies by product and formulation.
No for interior paint outside — interior formulations lack the UV inhibitors, mildewcides, and flexibility needed to withstand weather. Interior paint outdoors will fade, peel, and fail within one season. Exterior paint inside is technically possible but not recommended — exterior paints contain higher levels of VOCs (volatile organic compounds) and biocides that require significant ventilation indoors. Always use paint formulated for the intended environment.