Paint Coverage Calculator — How Far Does a Gallon Go?
Work out how much area your paint will cover and how many litres or gallons you need. Enter wall dimensions, pick the number of coats, and get the amount to buy with sensible can sizes — no half-used tins.
How paint coverage is calculated
- 1Wall area: (2 × length + 2 × width) × height
- 2Subtract doors (approx. 1.8 m² each) and windows (approx. 1.2 m² each)
- 3Add ceiling area if painting: length × width
- 4Amount needed: area ÷ spreading rate × number of coats
- 5Spreading rate varies: matte paint 10–12 m²/L, gloss 8–10 m²/L, primer 6–8 m²/L
- 6Round up to the nearest can size to avoid partial-tin waste
Worked example
Bedroom: 4 × 3.5 m, walls 2.4 m high, one door and one window. Two coats of matte emulsion (11 m²/L).
Wall area: 36.0 m² − 3.0 m² openings = 33.0 m². Two coats: 66.0 m² ÷ 11 = 6.0 L. Buy two 3 L tins or one 5 L tin plus one 1 L tin.
Frequently asked questions
How much does a gallon of paint cover?
A US gallon (3.78 L) of typical wall paint covers roughly 38–45 m² (400–480 sq ft) in one coat at a 10–12 m²/L spreading rate. Always check the product data sheet — coverage varies by paint and surface.
How many m² does a litre of paint cover?
Typically 10–12 m² per litre for matte and eggshell wall paint. Gloss and satinwood cover 8–10 m²/L. Primer covers 6–8 m²/L.
How many coats of paint do I need?
New plaster or a big colour change: 3 coats (primer + 2 top coats). Repainting a similar colour: 2 coats. Same colour refresh: 1–2 coats.
Does textured surface change paint coverage?
Yes — rough or porous surfaces (new plaster, textured render, bare wood) absorb more paint and can reduce coverage noticeably. Use primer first and expect the lower end of the spreading-rate range.