How Much Paint Do I Need? Paint Coverage Per Litre & Gallon

"How much paint do I need?" is the single most common painting question, and the answer everyone wants — a single number — is the one nobody can honestly give. Paint coverage is not a fixed figure. It depends on the paint, the surface, the colour underneath, the applicator and even the weather. But once you know what drives the number, estimating it accurately becomes straightforward.

The headline numbers

As a working rule of thumb that holds up across most interior emulsions on a prepared wall:

• 1 litre of interior wall paint covers roughly 10–12 m² on the first coat and 12–14 m² on the second.
• 1 US gallon (3.785 L) covers roughly 350–400 sq ft on the first coat.
• Primer covers about 8–10 m² per litre on porous surfaces.
• Exterior masonry paint covers only 4–8 m² per litre because brick and render are thirsty.

These ranges are wide for a reason. The HeavenHome calculator applies the right rate for each paint type automatically, but it helps to understand why the number moves around.

What increases paint consumption

Five things make a wall drink more paint than the headline figure suggests:

1. Porous surfaces. Bare plaster, new drywall, unprimed render and untreated brick all soak up the first coat aggressively. Always prime these surfaces — a £15 tin of primer can save two litres of topcoat.
2. Dramatic colour changes. Painting a light colour over a dark one always needs more coats. Deep reds, navy blues and charcoal greys are notorious for poor opacity because they use tint pigments instead of titanium dioxide for coverage.
3. Rough or textured finishes. A pebble-dashed wall has far more real surface area than its flat measured dimensions suggest — sometimes 50–100% more. Multiply the painted area by a surface factor of 1.3–2.0 to allow for this.
4. Thin application. Over-thinning paint, using a short-nap roller on a textured wall or rolling too fast all lay down less paint per square metre, which means more coats.
5. Hot, dry or windy conditions. Paint that skins over too quickly cannot flow out, so you tend to apply more to get a flat finish — especially relevant outdoors.

What decreases paint consumption

Conversely, you will use less paint than the headline figure when the surface is already sealed and smooth, when the colour change is subtle, and on the second and subsequent coats. This last point matters more than most people realise: the first coat does most of the absorption work, so by the time you apply a second coat the wall is sealed and the paint spreads further. Our calculator applies a 0.8× factor to additional coats to reflect this, which is why two coats do not simply double your paint requirement.

Coverage by paint type — quick reference

Converting between metric and imperial

Paint tins are labelled differently around the world, which catches people out. The conversions that matter are: 1 US gallon equals 3.785 litres (1 imperial gallon equals 4.546 litres — a meaningful difference), and 1 square metre equals 10.764 square feet. Our calculator handles all of these conversions internally and displays whichever unit you prefer, but if you are working by hand it is worth double-checking whether a "gallon" figure refers to US or imperial gallons before you commit.

Putting it into practice

The reliable way to estimate coverage is to start with the right rate for your paint and surface from the table above, then adjust for any of the five consumption factors that apply to your project. The calculator does this for you in seconds, and shows the working in the room-by-room breakdown so you can see exactly where each litre is going. If the result looks high, check whether you have selected the right paint type — a common slip is leaving the default interior matte selected when you are actually painting exterior render.