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Paint calculator: liters, gallons, and cans
Estimate how many liters or gallons of paint and how many cans you need to buy to paint your walls. Enter the room dimensions or the total area, subtract doors and windows, and adjust the coats, coverage, and waste. Works in metric (Europe/LatAm) or American (US) units.
Last reviewed: July 2026 · How we calculate
Input data
Adjust it based on the product label.
Results
Enter the data and press Calculate.
Results are estimates. Always verify manufacturer or supplier specifications before buying.
How to calculate the paint you need
Calculating the paint for a room is, at its core, calculating a surface area and converting it into liters (or gallons) and the cans you will have to buy. This calculator does all the work for you, but it helps to understand the steps so you can check that the result makes sense:
- Wall area. It is obtained from the room perimeter multiplied by the height: 2 × (length + width) × height. If you prefer, you can enter the total area directly in square meters or feet.
- Subtracting openings. Doors and windows are gaps that are not painted, so their surface is subtracted from the total. The tool subtracts an average value for each door and each window.
- Coats, coverage, and waste. The area to paint is multiplied by the number of coats, a waste margin is added, and it is divided by the product coverage (how many square meters a liter covers). The result in liters is divided by the can size and rounded up, because you can't buy half a can.
Formula
With the room dimensions, the full calculation is:
Area to paint = Area − (doors and windows)
Liters = Area to paint × Coats × (1 + Waste ÷ 100) ÷ Coverage
Cans = round up( Liters ÷ Liters per can )
The opening deduction is automatic: each door subtracts 1.9 m² (20 ft²) and each window subtracts 1.2 m² (12 ft²). These are average values; if your doors or windows are larger, you can use the "Total area" mode and enter the already-deducted surface yourself. In American units, coverage is expressed in ft²/gal and the result in gallons.
Paint types and real coverage per coat
The coverage this calculator uses depends on the type of paint: an interior latex doesn't cover the same as an elastomeric coating. Typical references per coat on a smooth, sealed surface:
| Interior vinyl / latex | 10–12 m²/L (≈400–500 sq ft/gal) — interior walls and ceilings |
|---|---|
| Exterior acrylic | 8–10 m²/L (≈320–400 sq ft/gal) — façades; withstands sun and rain |
| Enamel (water- or solvent-based) | 12–14 m²/L — doors, metalwork, wood |
| Elastomeric / waterproofing | 1–2 m²/L — thick film; don't compare its coverage with regular paint |
Labels usually state coverage under ideal conditions. In practice, subtract 10–15% for texture, absorption, and application technique — or simply use the calculator's waste field. Rollers consume more paint than brushes on the first coat and less on later ones; sprayers lay a more uniform film but lose paint to overspray.
Practical example
Suppose a room of 4 × 3 m with 2.5 m height, with 1 door, 2 windows, 2 coats of paint, a coverage of 10 m²/L, 10% waste, and 4 L cans:
| Gross wall area | 2 × (4 + 3) × 2,5 = 35 m² |
|---|---|
| Minus openings (1 door + 2 windows) | 1 × 1,9 + 2 × 1,2 = 4,3 m² |
| Area to paint | 35 − 4,3 = 30,7 m² |
| Liters (2 coats, +10% waste) | 30,7 × 2 × 1,10 ÷ 10 = 6,75 L |
| 4 L cans | 6,75 ÷ 4 = 1,7 → 2 botes |
This is exactly the result you'll see if you press "Calculate" with the default values. If you reduced it to a single coat, 1 can would be enough; with 3 coats, consumption would rise to about 10.1 L and you would need 3 cans for the same room.
Coverage and coats tips
The coverage is the value that most affects the result. For interior latex paint, a typical value is 10 to 12 m²/L (around 350 ft²/gal) per coat, but enamels, waterproofing paints, and exterior paints cover less. 2 coats are recommended to achieve a uniform, opaque color; with a single one the base usually shows through. Keep in mind that new surfaces, unsealed plaster, or very porous walls absorb more paint and reduce the actual coverage, so a prior primer coat may be worthwhile.
The surface rules: preparation and absorption
Two identical rooms can consume very different amounts of paint depending on the wall's condition. Fresh, unsealed plaster absorbs the first coat almost entirely: applying sealer or primer costs less than that lost coat and evens out the surface. Rough or textured surfaces have more real area than what you measure with a tape — expect 20–30% higher consumption than on a smooth wall.
Color changes count too: covering a dark tone with a light one usually requires one full extra coat (add it in the calculator's coats field). And before painting, patch cracks and chips: each patch absorbs paint unevenly and shows in the finish if not sealed. Preparation isn't an extra — it's where the label's stated coverage is won or lost.
Common mistakes when calculating paint
- Forgetting the second coat. Calculating with a single coat leaves your budget short; you almost always need 2 for an even finish.
- Not deducting openings properly. Ignoring doors and windows inflates the calculation; over-deducting leaves you short on paint. Use the average values or measure your actual openings.
- Using a generic coverage. Every product covers differently. Take the value from the label instead of a number "from memory".
- Not rounding to whole cans. The store sells complete cans: if the calculation gives 1.7 cans, you need to buy 2.
Frequently asked questions
How many liters of paint do I need per square meter?
With a typical coverage of 10 m²/L per coat, one square meter uses about 0.1 L per coat. Since 2 coats are recommended, estimate around 0.2 L per square meter. The exact value depends on the coverage stated on the product label and the surface absorption.
Why should I account for waste?
A 10% margin covers real losses: paint left on the roller and brush, splatter, touch-ups, and surfaces more porous than expected. It's better to have a little left over than to run out of paint halfway through a wall and risk shade differences between batches.
How many coats of paint should I apply?
As a general rule, 2 coats are applied to achieve a uniform color and good coverage. On new, very porous surfaces, or when making a strong color change (for example from dark to light), you may need 3 coats or a prior primer coat.
How do doors and windows affect the calculation?
Doors and windows are gaps that are not painted, so their surface is subtracted from the total wall area. This calculator automatically deducts 1.9 m² (20 ft²) per door and 1.2 m² (12 ft²) per window, average values you can adjust by measuring your actual openings.
Is coverage the same for all paints?
No. Coverage changes based on the paint type, brand, and finish. Interior latex paints are usually around 10 to 12 m²/L, while enamels, waterproofing, or exterior paints cover less. Always use the value shown on the can label to fine-tune the calculation.
Should I buy exact cans or round up?
Always round up to whole cans, because you can't buy a fraction of a can. Having a little paint left over is useful for later touch-ups and avoids the risk that a new batch has a slightly different shade.