Paint Calculator

Calculate Paint

m
m

Paintable Area

45.3 m²

Total (×2 coats)

90.6 m²

Paint Needed

9.1 liters

@ 10 m²/L

How This Calculation Works

The paint calculator estimates how much paint you need by first computing the total wall area (wall length × height × number of walls), then subtracting openings like doors and windows. It uses standard opening sizes — roughly 1.9 m² (20 ft²) for a door and 1.4 m² (15 ft²) for a window — which match typical residential dimensions.

The net paintable area is then multiplied by the number of coats. Most interior paint jobs need two coats for even coverage, especially when changing colours. The total area is divided by the coverage rate of the paint — typically 10 m² per litre or 350 ft² per gallon for standard latex paint on smooth walls.

Textured surfaces, porous materials like bare drywall, and dark-to-light colour changes can reduce coverage by 20–30%, so consider adding extra paint in those situations.

Common Mistakes to Avoid

  • Forgetting the second coat. One coat rarely provides full coverage. Budget for two coats minimum — three if you are covering a dark colour with a lighter one.
  • Not subtracting openings. Doors and windows can account for 10–15% of wall area. Skipping them means buying more paint than necessary.
  • Ignoring surface texture. Brick, stucco, and heavily textured walls absorb more paint. Use the higher end of the coverage range or add 20% to your estimate.
  • Mixing batches. If you need multiple cans, buy them from the same batch to avoid subtle colour differences. Ask the store to shake them all for you.
  • Skipping primer. On new drywall, patches, or stains, primer is essential. Without it, you may need an extra coat of paint that would have been cheaper as primer.

Worked Example

Scenario: A bedroom measuring 4 m × 3.5 m with 2.4 m high walls. The room has 1 door and 2 windows. You want 2 coats of standard interior paint.

Step 1 — Total wall area: Perimeter = 2 × (4 + 3.5) = 15 m. Wall area = 15 × 2.4 = 36 m².

Step 2 — Subtract openings: 1 door (1.9 m²) + 2 windows (2 × 1.4 = 2.8 m²) = 4.7 m². Net area = 36 − 4.7 = 31.3 m².

Step 3 — Multiply by coats: 31.3 × 2 = 62.6 m².

Step 4 — Calculate paint: At 10 m²/L coverage, you need 62.6 ÷ 10 = 6.26 litres. Buy 7 litres (or two 4 L cans) to be safe.

Frequently Asked Questions

How much does one litre of paint cover?
On average, one litre of standard interior latex paint covers about 10–12 m² (100–120 ft²) on a smooth surface. High-quality paints and primer-and-paint combos may cover slightly more. Textured or porous surfaces reduce coverage significantly.
Do I really need two coats of paint?
In most cases, yes. Two coats ensure even colour, hide imperfections, and improve durability. One coat may suffice only if you are repainting the same colour with a premium paint. When switching from dark to light, three coats (or tinted primer + two coats) may be necessary.
Should I subtract doors and windows from the total area?
Yes. Standard doors and windows together can represent 10–15% of the wall area. Subtracting them gives you a more accurate paint estimate and prevents over-buying.
How do I estimate paint for textured walls?
For light texture, add 15–20% to the calculated amount. For heavy texture like brick or stucco, add 25–30%. The texture creates more surface area that absorbs paint.
Is leftover paint useful?
Absolutely. Keep leftover paint for touch-ups — walls get scuffed over time, and having matching paint saves a trip to the store. Store it sealed in a cool, dry place; latex paint lasts up to 10 years when stored properly.