How many coats should I use?

Two coats is common for most interior paint jobs. You may need more for strong colour changes, new drywall, or high-porosity surfaces. Always follow the paint manufacturer’s guidance.

Should I subtract windows and doors?

You can subtract large openings if you want a tighter estimate. Many people leave openings as 0 and use a waste allowance instead, especially if there will be touch-ups and cut-ins.

Why is my paint coverage different from the default?

Coverage depends on the product, sheen, substrate, and wall texture. The most accurate value is the coverage listed on your paint can or product datasheet.

Paint Calculator (Walls & Ceiling)

Paint Calculator

Estimate how much paint you need for walls and ceilings. Choose what you’re painting, subtract openings if you want, then apply coats, coverage rate, and a waste allowance for touch-ups.

Paint Calculator

Estimate paint for walls/ceiling using coats, coverage rate, and waste allowance

What are you painting?

Coats

Room length

Room width

Room height

Openings area (optional)

Coverage rate

Waste allowance

Results

Enter dimensions above to calculate

Formulas used

The calculator estimates total paint area, then converts that into litres or gallons using coats and coverage.

1. Calculate Paint Area

Formula:

Walls = 2 × (Length + Width) × Height | Ceiling = Length × Width

For a rectangular room, wall area is the perimeter multiplied by height. Add ceiling area if you’re painting it. For irregular rooms, calculate each section and use Custom Area.

2. Subtract Openings (Optional)

Formula:

Net Area = Gross Area − Openings Area

Subtract windows, doors, or large areas that won’t be painted. If you’re unsure, leave it as 0 and rely on waste allowance.

3. Apply Coats and Coverage

Formula:

Paint Needed = (Net Area × Coats) ÷ Coverage

Coverage varies by product and surface texture. Use the number printed on your paint tin or datasheet for best accuracy.

4. Add Waste Allowance

Formula:

Paint to Buy = Paint Needed × (1 + Waste%)

Waste covers roller loss, cut-ins, touch-ups, and porous surfaces. 5–15% is typical depending on conditions.

Example

Paint walls + ceiling in a 5 m × 4 m room, 2.4 m high. Subtract 4 m² of openings. 2 coats, 10 m²/L coverage, 10% waste.

Walls = 2 × (5 + 4) × 2.4 = 43.2 m²
Ceiling = 5 × 4 = 20.0 m²
Net area = (43.2 + 20.0) − 4.0 = 59.2 m²
Paint needed = (59.2 × 2) ÷ 10 = 11.84 L
Paint to buy = 11.84 × 1.10 ≈ 13.02 L

Frequently Asked Questions

How many coats should I use?: Two coats is common for most interior paint jobs. You may need more for strong colour changes, new drywall, or high-porosity surfaces. Always follow the paint manufacturer’s guidance.
Should I subtract windows and doors?: You can subtract large openings if you want a tighter estimate. Many people leave openings as 0 and use a waste allowance instead, especially if there will be touch-ups and cut-ins.
Why is my paint coverage different from the default?: Coverage depends on the product, sheen, substrate, and wall texture. The most accurate value is the coverage listed on your paint can or product datasheet.