Paint calculator — how much paint do you need?

Enter the room dimensions or the area directly, choose the number of coats and the paint’s coverage — and get the paint quantity in liters or gallons plus a suggested can breakdown.

m
m
m
m²

Doors and windows — an interior door is roughly 1.6 m², a window 1–2 m².

pcs

Two coats is standard for full coverage.

m²/l

Typically 6–10 m²/L — check the can.

Total painting area
59.2 m²
29.6 m² × 2 coats
Paint needed
7.4 liters
Suggested cans
3 × 2,7 l

Coverage varies with the substrate: smooth drywall often gets 8–10 m²/L while rough render and concrete can drop to 4–6 m²/L on the first coat. Buy one can extra — tinted colors can vary between batches.

The calculation is an estimate and does not replace engineering design or the supplier’s instructions. Always check against project documents, product data sheets and applicable codes.

How to work out the paint quantity

The wall area of a room is the perimeter times the ceiling height: 2 × (length + width) × height. Then deduct doors and windows — an interior door is roughly 17 sq ft (1.6 m²) and a typical window 10–20 sq ft (1–2 m²). A 13 × 10 ft room with 8 ft ceilings has 2 × (13 + 10) × 8 = 368 sq ft of wall; with 40 sq ft of openings, about 328 sq ft remains to paint.

Paint quantity is painting area × number of coats ÷ coverage. With two coats and 350 sq ft/gal, the example above works out to 328 × 2 ÷ 350 ≈ 1.9 gallons — in practice two 1-gallon cans. Buy slightly more than the math says: tinted colors can vary a little between mixing batches, and leftovers are worth keeping for touch-ups.

The substrate decides the consumption

The coverage printed on the can normally assumes a smooth, previously painted surface. Rough render, bare concrete and textured wallpaper have more actual surface area and soak up more paint — expect 20–40% higher consumption on the first coat. New and patched surfaces should always be primed first; primer is cheaper than topcoat and evens out absorption so the finish dries to a uniform sheen without visible joints.

Sheen matters too: flat and matte finishes hide imperfections and suit ceilings and low-traffic walls, while satin and semi-gloss are tougher and washable for kitchens, hallways and trim. Higher sheen is more durable but reveals more of the substrate — the smoother the wall needs to look, the more preparation it takes.

Frequently asked questions

How much area does a gallon or liter of paint cover?
Typical wall paint covers 300–400 sq ft per gallon, or 6–10 m² per liter, on a smooth, previously painted surface. Rough render, bare concrete and other porous substrates can drop to 200–250 sq ft/gal (4–6 m²/L) on the first coat. The exact coverage is always printed on the can.
Is one coat of paint enough, or do I need two?
Plan on two coats for full coverage — that is the standard and gives an even color and sheen. One coat can be enough if you repaint in the same or a very similar color with a high-hiding paint. Dramatic color changes, like dark red to white, may need three coats or a tinted primer first.
Do I need primer on new surfaces?
Yes. New drywall, skim-coated patches, bare wood and other porous substrates should always be primed. Primer evens out how much the surface absorbs so the topcoat dries to a uniform sheen and color — without it, joints and filler repairs often telegraph through the finished result.
What paint sheen should I choose?
Flat hides surface imperfections best and is the usual choice for ceilings. Matte or eggshell is standard for living room and bedroom walls. Satin stands up to wiping and suits hallways, kitchens and kids’ rooms. Semi-gloss is used on trim, doors and casings that see hard wear. The higher the sheen, the tougher the surface — but the more it reveals every bump in the substrate.
How much paint do rough surfaces like render and concrete need?
Rough substrates have more actual surface area and absorb more — expect 20–40% higher consumption on the first coat compared with smooth drywall. After priming or the first coat, consumption drops back to normal levels.

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