Exterior Paint Calculator

About Exterior Paint Calculator

Exterior painting needs more paint per square metre than interior work, and the usual mistake is estimating it with an interior coverage figure. This calculator starts at 7 square metres per litre rather than 10, because masonry, render and pebbledash are porous and textured, and both properties increase how much paint a surface takes. Rough render can drop below 6, and bare or previously unpainted masonry lower still, because the first coat is partly absorbed rather than sitting on the surface. That first coat on new render behaves more like a primer than a finish, which is why two coats is the minimum outdoors and three is common on anything previously unpainted. The measurement itself works the same way as interior walls: the perimeter multiplied by the height, minus doors and windows, which are worth deducting outdoors because exterior windows are usually much larger than interior doors. Check the coverage printed on your tin and enter it rather than relying on the default, since exterior products vary far more than interior emulsion. For a fence see Fence Paint Calculator.

How to use Exterior Paint Calculator

  1. Enter room length, width, and wall height in metres
  2. Set the number of doors and windows to subtract their area
  3. Choose number of coats and see litres and gallons needed

Frequently Asked Questions

How much does exterior masonry paint cover?
Typically 6 to 8 square metres per litre on smooth render, against about 10 for interior emulsion. Rough or textured surfaces such as pebbledash can drop below 6, and bare masonry absorbs more still on the first coat.
How many coats does exterior paint need?
Two as a minimum, and three on bare or previously unpainted masonry where the first coat is largely absorbed. Skimping outdoors shows quickly, since the finish is exposed to weather and UV rather than sitting in a protected interior.
Should I deduct windows and doors outside?
Yes, and it matters more than indoors because exterior windows are usually large. A house with big windows can have twenty percent less paintable wall than the raw perimeter calculation suggests.
Does the surface texture really change the amount?
Considerably. Texture increases the actual surface area well beyond the flat measurement, so pebbledash or heavily textured render can use half again as much as smooth render for the same wall dimensions.
Can I use interior paint outside if I add more coats?
No. The difference is in the binder and the additives that resist UV, rain and mould, not in the thickness. Interior emulsion outdoors fails within a season regardless of how many coats you apply.

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