Paint calculator

Paint Calculator

Estimate how much paint you need for walls, rooms, ceilings and exterior surfaces.

Measurement system Metric (metres and litres) Imperial (feet and US gallons)

Surface to paint Room walls Single wall Ceiling Exterior walls

Room dimensions

Room length (m)

Room width (m)

Wall height (m)

Wall dimensions

Wall width (m)

Wall height (m)

Ceiling dimensions

Ceiling length (m)

Ceiling width (m)

Exterior wall dimensions

Total wall perimeter (m)

Average wall height (m)

Enter the total perimeter of the exterior walls, not the floor area. For irregular buildings, add the lengths of all exterior wall sections.

Openings and paint requirements

Number of doors

Number of windows

Area per door (m²)

Area per window (m²)

Number of coats 1 coat 2 coats 3 coats 4 coats

Extra paint allowance (%)

Paint coverage (m²/L)

Paint price per litre (optional)

Coverage varies by paint brand, surface texture, application method and colour. Check the paint tin for its stated coverage.

Estimated paint required

—

US gallons: —

Paintable area: —

Estimated paint cost: —

Enter dimensions to calculate your estimate.

Paint Calculator Formula

Paintable area = Total surface area − Area of doors and windows

Paint required = (Paintable area × Number of coats ÷ Paint coverage) × (1 + Waste allowance ÷ 100)

For a room with four walls, the total wall area is calculated as twice the sum of the room's length and width, multiplied by the wall height.

Worked Example

Painting a room

Suppose a room is 5 m long, 4 m wide and 2.8 m high.

Wall area = 2 × (5 + 4) × 2.8 = 50.4 m².

Assume one door of 1.8 m² and two windows of 1.2 m² each.

Paintable area = 50.4 − 1.8 − (2 × 1.2) = 46.2 m².

For two coats, coverage of 10 m²/L and a 10% allowance:

Paint = (46.2 × 2 ÷ 10) × 1.10 = 10.164 litres.

Round up to a suitable available paint container size.

Frequently Asked Questions

How much paint do I need?

It depends on the total surface area, paint coverage, number of coats and surface condition. Measure the surfaces, subtract openings where appropriate, and use the coverage rate printed on the paint container.

How many square metres does one litre of paint cover?

Coverage varies by product. This calculator uses an adjustable default of 10 m² per litre. Replace it with the manufacturer's stated coverage for a more accurate estimate.

How many gallons of paint do I need?

Enter your dimensions in feet and coverage in square feet per US gallon. The calculator estimates the required volume in US gallons and litres.

Should I subtract doors and windows?

For wall calculations, subtract the area of doors and windows that will not be painted. If you plan to paint those surfaces too, adjust the opening counts accordingly.

How many coats of paint should I use?

The required number of coats depends on the paint, surface, colour change and manufacturer's directions. Two coats are a common starting estimate, but follow the product instructions.

Is the paint cost exact?

No. The cost is an estimate based on the price you enter and the calculated paint volume. Actual purchases may vary because paint is sold in fixed container sizes, and primer, tools and labour are not included.