What This Calculator Does

The Paint Calculator estimates four walls and an optional ceiling in a rectangular room. It deducts the total openings area, applies the coat count and uses the product coverage you enter. Results include litres, US gallons, whole buckets and optional material cost.

When to Use It

Use it for an initial purchase estimate for room walls, the ceiling or both. Multiple rooms must be calculated separately. For flooring use the flooring calculator; for volume alone use the volume converter. This is not a general multi-region wall-measurement tool.

Inputs Explained

Length and width must be positive; height is needed when walls are selected. Feet use ft² for openings and coverage; metres use m². Openings must be non-negative and smaller than the chosen gross area. Coats are an integer from 1 to 20. Enter the specific product’s coverage per single coat per litre or US gallon and its bucket volume. Neither is supplied as a universal default. Price is optional.

Measure each opening separately and add its area once. When both walls and ceiling are selected, the entered total is deducted from their combined area; use openings that belong to that selected job.

Product labels may describe coverage per litre per coat or total coverage per bucket. This tool requires single-coat coverage per selected volume unit. If a five-litre bucket covers forty square metres for one coat, enter eight square metres per litre, then enter the bucket size and coat count separately.

How the Calculation Works

Walls = 2×(length+width)×height. Ceiling = length×width. Net area = selected gross area−openings. Total coated area = net area×coats. Paint volume = coated area/coverage. Buckets = ceiling(volume/bucket size). A US gallon is 231 in³, equivalent to 3.785411784 L.