Coverage is per coat
The coverage on a paint label, also called the spreading rate, tells you how much surface one liter or one gallon covers in one coat. In the US it is usually given in square feet per gallon, often as a range such as 350 to 400 sq ft. In the UK and much of Europe it is given in square meters per liter, often as “up to” a number, for example up to 12 m²/L.
Two coats need twice the paint. The amount for each surface is:
paint = area × coats ÷ coverage per coat
Example: 28 m² of wall, an example coverage of 10 m²/L, two coats: 28 × 2 ÷ 10 = 5.6 L. One coat would be 2.8 L. The example uses 10 m²/L rather than an “up to 12” label figure because, as the next section explains, that figure is a best case.
Why the label is a starting point
The label figure is usually a best case, on a smooth, sealed surface at the intended thickness. Real walls often take more. How far the paint goes depends on:
- The surface. Fresh plaster, bare wood and patched areas soak up paint. Textured walls, textured wallpaper and rough stucco have more surface than their flat measurements suggest.
- The color change. Going from dark to light, or covering a strong color, may need an extra coat.
- The product. Coverage differs between ranges of the same brand, and between finishes.
- How it is applied. Rollers with a long nap, spraying and back-rolling all change how much ends up on the wall.
If the label gives a range, using the lower end is the cautious choice. “Up to” figures are a best case. The waste allowance (10% is a common starting point) then covers rollers, trays and touch-ups. If you are unsure whether a surface needs a sealer, stain blocker or a special primer, follow the manufacturer’s instructions; this site does not assess surfaces.
How many coats
Two coats are a common plan for walls and ceilings; check what your product’s label says. One coat may be enough when you repaint in a similar color over a sound surface with a product that is sold for one-coat use. Three may be needed over a strong color. Enter the number of coats you plan; the paint calculator accepts 1 to 10.
First coat and later coats
Some labels give two figures: a lower coverage for the first coat on a bare, porous or weathered surface, and a higher one for the coats after it. Then the coats are not equal, and the amount is:
amount = area ÷ first-coat coverage + (coats − 1) × area ÷ later-coat coverage
Example: 20 m², two coats, a label that says 6 m²/L for the first coat and 10 m²/L after it: 20 ÷ 6 + 20 ÷ 10 = 3.33 + 2 = 5.33 L. One figure of 10 m²/L for both coats would have said 4 L.
The deck, fence and patio stain calculator takes both figures: the coverage per coat and an optional coverage for later coats. A Floor finish (clear varnish, polyurethane or floor oil) in the paint calculator also takes an optional coverage of the first coat. Paint and primer use one coverage for every coat, in the paint calculator and in the exterior paint calculator; if your paint label gives two, the cautious choice is to enter the lower, first-coat figure for every coat.
Primer is a separate material
Primer is not “one more coat”. It has its own coverage, often lower than the topcoat, and it is a different product from a different can. In the planner it is a separate material.
Example: the same 28 m² wall, one coat of a primer with an example coverage of 10 m²/L: 28 × 1 ÷ 10 = 2.8 L; with 10% allowance 3.08 L, which in 2.5 L cans is 2 cans (5 L, about 1.92 L left). The two topcoats are calculated on their own line.
The same goes for colors and finishes: walls in one color and a ceiling in white are two materials. Their amounts are never added together, because leftover white cannot finish the walls.
Gallons, quarts and liters
- US gallon: 128 US fluid ounces, 3.785 liters. A US quart is a quarter of that, about 0.946 L.
- Imperial gallon: 4.546 liters, about 1.2 US gallons. It is rarely used for paint today, but older guides and some cans mention it. Coverage per US gallon and per imperial gallon are not the same number.
- Liter: the usual unit outside the US, with common can sizes such as 1 L, 2.5 L and 5 L.
For orientation only: 350 sq ft per US gallon is about 8.6 m² per liter, and 10 m² per liter is about 407 sq ft per US gallon. Products sold in different countries are different paints, so use the label in front of you rather than a converted figure.
Not every gallon holds 128 fl oz
Some tint bases are deliberately filled with less than a full gallon so that colorant can be added at the store. Reported fills such as 116 fl oz are about 9% less than a full gallon. Look at the fill printed on the can and enter the real fill as the can size: 116 fl oz is 0.906 US gal or about 3.43 L.
It matters at the rounding step. If a job needs 2.8 gallons, three full gallons cover it. With 116 fl oz cans entered as 0.906 gal, 2.8 ÷ 0.906 = 3.09, so you need four cans. See how pack rounding works.
Putting it together
- Measure the walls and openings (how to measure a room).
- Take coverage per coat from the label, using the cautious end of any range.
- Paint = area × coats ÷ coverage, for each surface.
- Add up surfaces assigned to the same paint entry; keep colors, finishes and primer apart.
- Add the allowance, then round up to whole cans of the real fill.
The paint calculator and the room refresh planner do these steps for you once you have the numbers.