Paint Calculator

What Is a Paint Calculator?

A paint calculator is a tool for estimating the quantity of paint required to cover a surface. It uses the dimensions of the area being painted, the number of coats and the paint's coverage rate to calculate an estimated amount of paint in litres.

This paint calculator can be used for walls and similar large surfaces. It allows you to account for doors, windows and other areas that will not be painted, as well as an additional allowance for waste. You can also enter a paint container size to estimate the number of complete tins or tubs required.

Why Use a Paint Calculator?

Estimating paint requirements before starting a decorating project can help with purchasing decisions and provide a useful quantity estimate before buying materials.

How to Use the Paint Calculator

Measure the walls or surfaces you intend to paint before entering the dimensions into the calculator.

1. Enter the wall length — Enter the length of a wall and choose the appropriate measurement unit.
2. Enter the wall height — Enter the height from the floor to the ceiling or the height of the surface being painted.
3. Enter the number of walls — For walls of the same dimensions, enter the number of walls that will be painted.
4. Subtract doors and windows — Enter their combined area in square metres if these surfaces will not be painted.
5. Enter the number of coats — Select how many coats you intend to apply.
6. Enter paint coverage — Use the coverage stated on the paint manufacturer's product information, measured in square metres per litre.
7. Add a waste allowance — Select an appropriate percentage for additional paint requirements.
8. Calculate the result — The calculator displays the estimated surface area and amount of paint required in litres.

How Much Paint Do I Need?

The amount of paint required depends primarily on the surface area, number of coats and coverage rate of the paint. To estimate the quantity, calculate the paintable surface area, multiply it by the number of coats and divide the result by the paint's coverage in square metres per litre.

For example, if a room has 40 m² of paintable wall surface and requires two coats, the total coverage requirement is 80 m². If the selected paint covers 10 m² per litre, approximately 8 litres are required before any additional allowance is included.

How Paint Coverage Affects the Calculation

Paint coverage is normally stated by the manufacturer in square metres per litre. A product with a coverage rate of 10 m² per litre theoretically covers 10 square metres with one litre under the stated conditions. Actual coverage can vary depending on the surface, application method, paint type, texture, porosity and other factors.

Why Paint Waste Should Be Considered

Not all paint purchased will necessarily reach the wall. Paint can be lost during application, remain in rollers and brushes, spill, or be left in containers. Surfaces with high porosity or texture can also affect practical coverage. A modest additional allowance can therefore provide a useful margin when estimating the amount to purchase.

Paint Calculator Formula

The calculator uses the following basic calculations to estimate the amount of paint required.

The result is an estimate rather than a guarantee of actual paint consumption. Paint coverage stated by manufacturers is normally based on particular conditions, and real-world results can differ because of surface preparation, texture, porosity, application method and the contrast between existing and new colours.

For rooms where the walls have different dimensions, calculate the area of each wall separately and add the results together before subtracting doors and windows. For ceilings, calculate the ceiling length multiplied by its width and add the resulting area to the other surfaces being painted.

Always check the paint manufacturer's instructions and product information before purchasing or applying paint. Primer, mist coats, specialist coatings and additional preparation may change the amount of material required.

Frequently Asked Questions