Worked example

Paintable area1,500 ft²
Coverage350 ft²/gal
One coat + 10%4.7 gal
Two coats + 10%9.4 gal
Gallons = surface area × coats × (1 + waste %) ÷ coverage per gallon

First define what 1,500 square feet means

Floor area and wall area are not interchangeable. A 1,500 ft² home can have much more than 1,500 ft² of wall surface because layout, ceiling height and room count add perimeter.

If 1,500 ft² is already the measured paintable wall or ceiling area, it can go directly into the formula.

Coverage is a range, not a constant

A common planning figure is 350–400 ft² per gallon for one coat on a smooth, prepared surface. Product labels take precedence.

At 350 ft² per gallon, one coat plus 10% needs 4.7 gallons and two coats need 9.4 gallons. Round to purchasable can sizes.

  • New drywall and porous surfaces can absorb more
  • Textured walls reduce practical coverage
  • Spraying can create more overspray loss

Separate wall paint, ceiling paint and primer

Different products should not be pooled into one total. Calculate each surface group separately because coverage, finish and can size may differ.

This also makes it easier to compare scenarios and avoid buying an unusable mix of partial quantities.

Use your numbers

Turn the example into your estimate.

The calculator keeps every assumption visible and updates the result as you type.

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