Paint Coverage Calculator
Gallons (2 coats)
2.86
Est. cost @ $30/gal
$85.71
How it works
Estimating how much paint to buy is one of the most common DIY calculations — and getting it wrong costs money. Too little means a second trip to the hardware store mid-project; too much wastes expensive product. The Paint Coverage Calculator estimates the litres or gallons needed for any room, surface, or project based on area, number of coats, and the paint's stated coverage rate.
**Coverage rates** Typical interior paint: 10–12 m² per litre (coverage varies by paint type, surface texture, and application method). Primer: 8–10 m²/litre (heavier body). Exterior paint: 8–10 m²/litre (slightly lower due to surface absorption). Gloss and semi-gloss: 10–12 m²/litre. Textured paint: 6–8 m²/litre.
**Calculating room area** For a rectangular room: wall area = 2 × (length + width) × ceiling_height. Subtract door area (standard interior door: 0.81m × 2.03m ≈ 1.64 m²) and window area (typical window: 0.9m × 1.2m ≈ 1.08 m²). Ceiling area = length × width. Total = wall area − door/window cutouts + ceiling area (if painting ceiling).
**Coverage waste factor** Apply a 10–15% waste factor for cutting in (brushwork at edges), roller nap coverage variation, and surface absorption on new drywall (which absorbs significantly more paint than previously painted surfaces). The calculator applies 10% waste by default and lets you adjust.
**Number of coats** One coat over matching colour: sometimes sufficient for touch-ups. One coat over white: typically requires two coats for dark colours. Two coats: standard for most interior paint jobs. Drastic colour change (dark to light or vice versa): may need a primer coat + two finish coats. The calculator multiplies area by the number of coats.
Privacy: all calculations run in the browser. No data is transmitted.
Frequently Asked Questions
- A 12×12 ft (3.66m × 3.66m) room with 8 ft (2.44m) ceilings: perimeter = 4 × 12 = 48 ft = 14.63m; wall area = 48 × 8 = 384 sq ft = 35.7 m². Subtract 2 doors (≈35 sq ft = 3.25 m²) and 2 windows (≈24 sq ft = 2.23 m²): net wall area ≈ 325 sq ft = 30.2 m². At 350 sq ft/gallon (typical coverage): 325/350 ≈ 0.93 gallons — buy 1 gallon for one coat. For two coats: 1.86 gallons — buy two 1-gallon cans. Ceiling (12×12 = 144 sq ft) adds another ~0.4 gallons.
- Rolling wastes less than brushing but still leaves material on the roller nap, tray, and as spatter. Typical waste factors: roller application on smooth walls: 5–8%. Textured or porous surfaces (new drywall, rough plaster): 10–15% extra absorbed by surface. Cutting in around edges with a brush: brush retains ~10% of loaded paint. Total recommended waste allowance: add 10% to calculated coverage for smooth surfaces, 15% for textured/porous surfaces, and 20% for first coat on fresh drywall (priming strongly recommended to reduce absorption).
- Primer is recommended (or required) for: new drywall (seals porous surface — without primer, uneven absorption causes visible 'flashing' in the finished paint). Bare wood (seals grain, prevents tannin bleed-through). Major colour changes (very dark to very light, or vivid colours over white). Stained or water-damaged areas (stain-blocking primer). Fresh plaster (alkaline surface damages some paints without an alkali-resistant primer). If painting over a clean, previously painted surface of similar colour, primer is usually unnecessary — a first coat of the new colour serves the same purpose.
- Flat/matte: no sheen; hides surface imperfections; not washable; best for ceilings and low-traffic areas. Eggshell: slight sheen; more washable than flat; popular for living rooms and bedrooms. Satin: moderate sheen; washable and durable; good for kitchens, bathrooms, children's rooms. Semi-gloss: visible sheen; very washable; standard for trim, doors, and window frames; highlights surface imperfections. High-gloss: very shiny; most durable and washable; used for doors, cabinetry, high-wear surfaces. Higher sheen = more washable but shows more surface imperfections.