Read paint coverage and plan for more than one coat
Understand per-coat coverage, allowances and full-can rounding using a clearly labelled test example.
A coverage number describes how much surface a stated quantity of paint covers under the conditions on the label. It is not a universal property of every paint. Surface preparation, texture and application conditions can change actual consumption.
Check the basis of the coverage figure
The tool expects area per unit volume for one coat: m²/L or ft²/US liquid gallon. Read the technical information for the actual product. A figure stated for a complete two-coat application cannot be entered as a one-coat figure without conversion. For example, 5 m²/L for two coats corresponds mathematically to 10 m²/L per coat if the same stated application basis applies. Confirm that basis rather than inferring it from a large number on the can.
US liquid gallons and imperial gallons differ. Our interface explicitly uses US liquid gallons. Convert an imperial-gallon label before entering it; switching the website to feet does not establish the gallon type on a manufacturer's label.
Separate coats, allowance and purchase rounding
Theoretical volume is paintable area × coats ÷ coverage per coat. The entered allowance then increases that volume. Rounding to whole cans happens after the volume is combined for a product. These are three different operations, and the result shows them separately.
Test inputs: 31 m², two coats, 10 m²/L per coat.
Theoretical need = 31 × 2 ÷ 10 = 6.20 L.
Entered allowance 10% gives 6.82 L.
With no usable paint owned and 2.5 L cans, ceil(6.82 ÷ 2.5) = 3 cans, or 7.5 L purchased.
10% and 10 m²/L are example inputs, not recommendations. If you choose 0% allowance, enter zero explicitly. A blank field means the assumption has not been confirmed.
Primer and existing paint
Primer is not automatically included as one of the finish coats. Create a separate product and use its own coverage and coats if you want a primer estimate. Paint already owned must be usable and compatible with the intended product, colour and finish; the tool does not inspect or certify it.
For the test above, 1 L of usable matching paint reduces the purchasing shortage to 5.82 L, which still requires three 2.5 L cans. Owned volume and whole-can purchase quantity are deliberately shown separately.
Calculate paint quantities or read how to combine rooms before rounding.
Sources and scope
For definitions of wallpaper match, repeat and packaging, see Brewster's product properties and Graham & Brown's wallpaper FAQ. Product instructions take precedence over generic examples. Unit conversions use the exact international foot (0.3048 m) and US liquid gallon (3.785411784 L); see NIST conversion factors.