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Exterior Paint Calculator

An exterior paint calculator works out how many gallons you need to paint a house exterior, from the wall area minus the doors and windows, the coverage rate and the number of coats. Exterior jobs are almost always two coats, and surface texture changes coverage a lot.

Your measurements

Result

Enter the perimeter and wall height (or the area), deduct the openings, and it returns the gallons — with a coverage figure you can drop for stucco, masonry or rough timber that drinks paint.

How it is calculated

Net wall area = gross wall area − openings. Gallons = net area × coats ÷ coverage per gallon. Smooth siding covers ~300-400 sq ft per gallon; stucco, masonry and rough timber drop to ~200-250 and may need extra on the first coat. Trim and primer are estimated separately.

Steps

Enter the house perimeter and wall height, or total wall area.
Deduct the square footage of doors and windows.
Set the coverage per gallon (lower for textured surfaces).
Enter the number of coats (usually two).
Read the gallons; buy primer and trim paint separately.

Worked example

A 150 ft perimeter at 10 ft high is 1,500 sq ft; less 120 sq ft of openings, at 325 sq ft/gallon and 2 coats, needs about 9 gallons.

Common questions

How much exterior paint do I need?

Net wall area × coats ÷ coverage. A 1,500 sq ft wall area at 2 coats is around 9 gallons. The calculator deducts openings.

How many coats for exterior paint?

Usually two over primer for durability and even colour, especially over a colour change or bare/repaired areas.

Why does coverage drop on stucco?

Texture has more surface area and soaks up paint, so rough surfaces cover far fewer square feet per gallon than smooth siding.

Do I need primer?

On bare wood, masonry, repairs or big colour changes, yes — estimate it separately at a similar coverage.