Paint Coverage Calculator Guide

Estimate gallons of paint by combining paintable area, number of coats, and the coverage rate for the product you plan to use.

Use the paint calculator

The ATHENA Paint Calculator calculates paintable wall area from room dimensions and subtracts approximate door and window area. You can add the ceiling, choose the number of coats, and enter the product's coverage per gallon.

Paint coverage formula

Paint needed = paintable area × coats ÷ coverage per gallon

For example, 700 square feet of paintable area with two coats and 350 square feet of coverage per gallon requires 4 gallons before any planning allowance.

How many gallons do I need?

Start with the total paintable area, multiply it by the number of coats, then divide by the product's stated coverage per gallon. Round the result up to a practical purchase quantity rather than assuming a partial gallon will always be available or sufficient.

Why coverage matters

Paint products vary. Surface texture, porosity, color changes, application method, and the product itself can change how much paint is actually used.

What coverage should I enter?

Use the manufacturer's coverage for the exact paint product whenever it is available. ATHENA starts with a 350 square-foot-per-gallon planning value, but you can replace it with the coverage printed on the product label.

What about a second coat?

Each additional coat increases the amount of paint required for the same paintable area. A two-coat project therefore uses roughly twice the coverage-based quantity of a one-coat project before accounting for waste, touch-ups, or surface conditions.

Ready to calculate?

Run your room numbers here: Free Paint Calculator.

How Much Paint Do I Need? · Paint Coverage Per Gallon Guide

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