Paint & Color

Work From Anywhere: Practical Online Opportunities in the USA, Canada and UK

Estimate the litres of finish paint needed for a rectangular room after doors and windows are removed.

Paint planning worksheet

Set the surface and paint assumptions for Work From Anywhere: Practical Online Opportunities in the USA, Canada and UK

Method for this tool

What the Work From Anywhere: Practical Online Opportunities in the USA, Canada and UK actually calculates

The calculation uses the perimeter of a rectangular room times its height, subtracts openings, and multiplies the remaining area by coats. It divides by coverage and adds your waste allowance. It excludes the ceiling, primer, and can-size rounding; coverage must reflect the product and surface you intend to paint.

The calculation path

Net wall area × coats ÷ coverage × (1 + waste percentage / 100) gives the paint volume.

Inputs that can change the answer

Room length: Enter room length in m.
Room width: Enter room width in m.
Wall height: Enter wall height in m.
Doors and windows: Enter doors and windows in m².
Coats: Enter coats as a number; use the definition in the calculation method.
Coverage per litre: Use the coverage per litre printed for the selected paint and surface, not the wall area.
Waste allowance: Percentage applied at the stage shown in the method; enter 10 for ten percent.

Checks that stay outside the formula

Check the coverage and coat system for the actual surface; waste is a separate chosen reserve.

A practical order for entering the data

Measure the room length, width, and common wall height in metres.
Add the areas of doors and windows you will not paint and enter that total as openings.
Enter the coat count, the paint's coverage per litre, and a waste percentage before checking the litres required.

Project walkthrough: From wall measurements to a paint shopping list

Engine check using the prefilled sample

Paint and colour example: room length = 4 m, room width = 3.5 m, wall height = 2.7 m, doors and windows = 4 m², coats = 2, coverage per litre = 10 m²/L and waste allowance = 10 %. Use these numbers to follow the calculation, then substitute the dimensions, coverage, coats, or preferences that match your room.

The four walls measure 2 x (4 + 3.5) x 2.7 = 40.5 square metres. Subtracting 4 square metres of openings leaves 36.5. Two coats at 10 square metres per litre need 7.3 litres; a 10% allowance brings that to 8.03 litres. Choose available can sizes that cover this amount, and estimate primer separately.

Results for these inputs

Paintable wall area: 36.50 m²
Paint required: 8.03 L

Project-specific method

Worked example and purchase checks

Start with geometry, not a litres guess. The page first calculates the perimeter of the rectangular room, turns that perimeter into gross wall area, removes openings, applies the real coat count, then divides by the coverage printed for the chosen paint. The waste percentage is applied only after the theoretical volume is known.

Illustrative worked example

A 12 × 14 ft bedroom converted to metres, with one door and one window excluded, two finish coats, and a paint rated at 9.5 m²/L.

Exact inputs for this example

Room length	4.27 m
Room width	3.66 m
Wall height	2.44 m
Doors and windows	3.2 m²
Coats	2
Coverage per litre	9.5 m²/L
Waste allowance	10 %

Paintable wall area: 35.50 m²
Paint required: 8.22 L

How to read the result

Use the litres as a planning requirement, then choose available can sizes that meet or slightly exceed it. Keep the coverage, coat count, and waste allowance beside the result so a later product change can be recalculated rather than guessed.

Assumptions this example makes

All four walls share the entered height.
Doors and windows entered under openings are not being painted with this product.
Coverage per litre is supplied by the visitor for the actual paint and surface.

What this calculator does not prove

It does not estimate primer, trim, ceiling paint, repairs, or mixed can-size purchasing.
Highly textured, porous, newly plastered, or strongly contrasting surfaces can use paint differently from the entered coverage.

Wall-area measurement sketchSketch is explanatory, not to scale.

Mistakes that change this result

Using floor area instead of wall area.
Subtracting openings twice—once in measurements and again in the openings field.
Treating the default 10 m²/L coverage as a product specification.