Exterior Coating Coverage Calculator

Estimate coating quantity from measured surface area, coats, and product coverage.

Inputs

Preset: Two-coat exterior paint

Two coats over 400 ft², with an assumed planning coverage of 325 ft² per US gallon and 1 gallon packages. This is an illustrative coverage rate; replace it with the exact product yield for your surface and application method.

Project area

Number of coats

Coverage per U.S. gallon

Formula, inputs and conditions

Formula: Project area*Number of coats/Coverage per U.S. gallon

Decimal results are displayed to two places when needed.

Inputs: Actual surface area, number of coats, product coverage per U.S. gallon for the substrate, and package volume.
Outputs: U.S. gallons and whole packages.
Conditions and scope: Deck stain, fence stain, paint, and asphalt sealer share a substrate/product model. The user supplies roughness and whether one or both sides are coated; there is no universal coverage rate. Results are planning estimates, not engineering, permit, code or contractor-price decisions.

Coats and coverage both matter

Paint coverage describes area per gallon for a particular product and surface. Two coats require covering the area twice. This tool first estimates liquid volume and can then round that volume into packages of your chosen size.

Measure and calculate

Measure the surface to be coated and subtract openings.
Enter the number of coats and coverage for the actual product and surface.
Use package mode if you need whole cans rather than theoretical gallons.

Calculation method

Gallons = surface area × coat count ÷ coverage per US gallon.

A worked example

Inputs: A 400 ft² surface needs two coats at an assumed 325 ft² per gallon.
Calculation: 400 × 2 ÷ 325 = 2.461538 US gallons.
Result: 2.46 US liquid gal

The displayed estimate is 2.46 US gallons. With 1 gallon packages, purchase mode rounds up to 3. The example coverage is an assumption to replace with product information.

Read the result

Output interpretation and next steps
Output or check	What it means for your project
Theoretical US gallons	Area times coat count divided by coverage gives the coating volume. The result can be fractional.
Whole packages	Package mode rounds the required volume upward using the entered package size. Product coverage must match the surface and application conditions.

Common questions

Is the entered area already multiplied by the coats?

Enter the physical surface area once. The calculator applies the coat count separately.

Can I use the same coverage for rough and smooth surfaces?

Only if the product information supports it. Texture, porosity and application method can change the appropriate coverage rate.