Paint Coverage Calculator
Estimate paint and whole cans from area, openings, coats and your product's coverage.
This tool runs entirely in your browser. Your data is never uploaded, never stored, and never leaves your device.
Paint Coverage Calculator deducts measured openings, applies your product's per-coat coverage and chosen allowance, then rounds up whole paint packs.
How to use it
- 1Choose metric or US customary units and enter a rectangle or measured total area.
- 2Deduct openings and enter the product coverage, coats, chosen allowance and one pack size.
- 3Calculate, inspect the assumptions and download the JSON quantity estimate if useful.
Example
- Input
- 5 × 4 m; 2 m² openings; 10 m²/L per coat; 2 coats; 10% allowance; 2.5 L packs.
- Output
- 18 m² net; 3.96 L with allowance; 2 packs = 5 L to purchase.
These are example choices, not a coverage or waste recommendation.
What happens to your data
Measurements and quantities are calculated in this browser without uploads or persistence. A downloaded estimate contains your entered measurements and assumptions.
Last updated October 2026
Paint coverage is not a single number that applies to every wall. A product's quoted coverage is usually an area per litre or US gallon for one coat, while your project may need several coats and may include surfaces that will not be painted. This calculator keeps those choices visible: measure a rectangle or enter the total gross area, subtract openings, supply the actual coverage and coat count, and choose a paint pack size.
The result separates paint before allowance, paint with your chosen extra allowance, and the amount purchased in whole packs. It is a quantity estimate rather than a product recommendation. No brand coverage, door size, window size or required waste percentage is silently assumed. The metric example is an arithmetic demonstration, not instructions for your paint or surface.
How it works
For a rectangle, gross area is length multiplied by width or wall height. For several walls, ceilings or other sections, measure them separately and enter their combined area in the measured-area mode. Excluded area is the total of openings or surfaces genuinely not being painted. Net area is gross area minus excluded area. An exclusion greater than the gross area is rejected, rather than silently changing the result to zero. An equal exclusion produces a valid zero-quantity estimate.
Paint before allowance equals net area multiplied by the number of coats and divided by the entered coverage per coat. Multiply that quantity by 1 plus the chosen allowance percentage divided by 100. The purchasing step divides by one pack size and rounds up to a whole pack. This does not optimize a mixture of different can sizes. Extra paint from full packs is shown separately from the allowance you selected. Calculate primer, trim, ceilings or products with different coverage separately.
Metric mode uses metres, square metres and litres. US customary mode uses feet, square feet and US liquid gallons, not UK Imperial gallons. Defined unit factors are applied with exact decimal fractions; integer pack decisions do not depend on a rounded display value. Inputs permit up to six decimal places without commas or exponent notation. The maximum surface is 1,000,000 m² equivalent, coats range from 1 to 20, and the chosen allowance ranges from zero to 100%. Results above 1,000,000 packs are rejected.
Changing units clears measurements, coverage and pack size so an old number cannot silently acquire a different unit. Editing a value clears the previous estimate and download. The JSON report records your active measurements, coverage, coats, allowance, pack size, assumptions and exact required-litre fraction. Calculations remain on your device; a report you choose to save contains those measurements. Displayed decimal volumes are approximate, while whole-pack rounding is exact for the supplied inputs.
Worked example: Separate paint allowance from full-pack surplus
- Input
- Rectangle 5 m × 4 m; openings 2 m²; coverage 10 m²/L per coat; 2 coats; 10% allowance; 2.5 L packs.
- Result
- 18 m² net; 3.6 L before allowance; 3.96 L with allowance; 2 packs = 5 L to purchase; 1.04 L extra from pack rounding.
Coverage, two coats and 10% are example choices, not recommended values for an unknown paint.
Common use cases
- Estimating one wall from its length and height before buying paint
- Combining measured surfaces using the same product and coat count
- Deducting doors and windows by their measured area instead of a guessed standard size
- Comparing a chosen pack size with the unrounded quantity and recording the assumptions
Frequently asked questions
Where should I get the coverage rate?＋
Use the label or technical information for the actual paint and surface. Coverage varies with porosity, preparation, texture, application method and colour changes. A quoted maximum may not be what your project achieves. This tool cannot identify the paint or validate its instructions.
Does the coverage field include all coats?＋
No. Enter area per litre or US gallon for one coat, then enter the number of coats separately. If a supplier gives a multi-coat system coverage, check its units before using it here; entering that number and multiplying coats again would count coats twice.
Can I calculate an entire room?＋
Yes, by adding the areas of the relevant walls and entering that sum in measured-area mode. Add a ceiling only if it uses the same product, coverage and coat count. The calculator does not guess room height, opening dimensions, skirting, trim or vaulted ceiling geometry.
What waste allowance should I select?＋
That is a project choice, not a universal recommendation. Follow your product information and purchasing plan, allowing for actual application loss or touch-ups where appropriate. Zero is accepted when you deliberately want no extra allowance; the example's 10% is not a prescription.
Why did changing the units empty my measurements?＋
A coverage of 10 m²/L is not the same as 10 ft²/US gallon. The fields are cleared deliberately so numbers are not reinterpreted without your consent. Enter measurements and product quantities in the newly selected units. Coat count and allowance remain unitless.
Is a result a guarantee that this much paint is sufficient?＋
No. It is the arithmetic result for your entered values and a single pack size. It does not inspect surfaces, specify coating systems or offer safety or structural advice. Confirm the measurements and the actual product instructions before purchasing.
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