Exterior Paint Calculator for Siding and Walls
Estimate paint for an exterior wall using its net area and your product's stated coverage on that surface.
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How to measure
Measure each exterior wall face and subtract large openings. Keep trim and siding separate if they use different products. Use the manufacturer’s exterior coverage range for your substrate rather than a single universal rate.
Formula and assumptions
Gallons = ((wall area − openings) × coats ÷ coverage per gallon) × (1 + allowance / 100).
Worked example
An 850 sq ft wall with 120 sq ft of openings, two coats, 350 sq ft per gallon and 12% allowance requires about 4.67 gallons.
Before you buy
Texture, bare masonry, primer and weather conditions can change actual coverage. Check the product technical sheet.
Do I need to count primer?
Yes, plan primer separately when the product or surface calls for it. This result estimates finish paint only.
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Editorial review: September 2026. This is a planning estimate; confirm dimensions and product specifications before purchase.