Paint Calculator

What this calculator does

Estimates paint in liters or US gallons for a flat surface from its width and height, the number of coats and the spreading rate printed on the tin.

How to use it

1. Measure the width and height of the wall in meters or feet, matching the selected system.
2. Enter the number of coats and the label coverage in m²/L (Metric) or ft²/US gal (Imperial).
3. Set a waste margin and read the liters or US gallons.

Formula

Area = Width × Height
liters = Area × Number of Coats / Paint Coverage × (1 + Waste Margin (%) / 100)

Formulas are shown in metric units, exactly as the calculator computes them. Imperial entries are converted to metric first. Waste is applied as a multiplier (1 + waste/100).

Areas are in m² and volumes in m³.

Variables

Worked example

Using the default values of this calculator (Width = 4 m, Height = 2.5 m, Number of Coats = 2, Paint Coverage = 10 m²/L, Waste Margin (%) = 10 %), the calculator returns:

Area = 4 × 2.5
liters = Area × 2 / 10 × (1 + 10 / 100)

• Paint Needed: 2.2 liters

Assumptions and limitations

• Doors and windows are not subtracted; get a net area from the Wall Area calculator first if needed.
• Coverage is for one coat. Use US gallons, not UK imperial gallons; convert the label rate if necessary.

Waste, rounding and buying

Round up to the next can size and keep a little for touch-ups. Buy all tins from one batch so the colour matches. Primer is a separate product.

Frequently asked questions

How much paint do I need for two coats?

Set coats to 2: the area is doubled before dividing by the coverage. Check the label coverage, because rough or porous surfaces take more.

How do I enter coverage in imperial mode?

Enter square feet per US gallon. For example, 10 m²/L is about 407.46 ft²/US gal. The calculator converts coverage to m²/L internally and displays paint in US gallons.

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• Wall Area Calculator
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• Drywall Calculator