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Exterior Paint Calculator

Works out exterior masonry paint. Coverage outdoors is much lower than indoors, and the surface texture matters more than anything else.

Total exterior wall area, with doors and windows already deducted.

Texture is the single biggest factor outdoors — pebbledash can take two and a half times what smooth render does.

coats

Two coats outdoors, always. The first is largely absorbed on anything textured.

m²/L

Set automatically from the surface above when you change it, or override here. Exterior coverage is far lower than interior because the surfaces are rougher.

Optional. Enter the price per litre or per US gallon.

Paint needed
— L

Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.

In US gallons — gal
Area to paint —
Per coat — L
Tins to buy —
Paint cost —
Reading this —

The formula

litres = area ÷ coverage per litre × coats

Coverage is the whole calculation, and it is the figure tins are most optimistic about. The label quotes a smooth, sealed, previously painted surface; bare plaster, textured render and a strong colour change all take noticeably more.

What to watch out for

Three things separate an exterior job from an interior one:

  • Texture dominates. Smooth render takes about 10 m²/L; pebbledash can be 4. That is a factor of two and a half on the same wall area.
  • The weather decides the day. Above 8 °C, dry, with a day clear afterwards, and out of direct sun. Hot walls skin the paint before it bonds.
  • Preparation is most of the work. Masonry paint over loose, chalky or algae-covered render fails in a season regardless of how much you apply.

Frequently Asked Questions

How much masonry paint do I need?

At 7 m²/L on light texture, a 90 m² wall takes about 26 litres for two coats. Smooth render would be closer to 18; pebbledash nearer 45.

How much paint does pebbledash take?

Roughly 4 m² per litre, against 10 for smooth render. A pebbledashed house can need two and a half times the paint of a rendered one of the same size.

What temperature can I paint outside at?

Above 8 °C and rising, with no rain forecast for 24 hours. Avoid direct sun on the wall you are painting — heat skins the surface before the paint has bonded underneath.

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