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Exterior Paint Calculator

Exterior Paint Calculator estimates exterior coating gallons for one façade or rectangular exterior wall surface. Enter job dimensions in U.S. customary units, adjust supplier assumptions, and get purchase-ready quantities instantly.

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HOW IT WORKS

Formula and assumptions

Multiply net surface area by coats, divide by coverage per gallon, and round the purchase quantity up.

Coverage is stated per coat on a smooth, prepared surface.
Gallons are rounded up for purchasing.

FIELD CHECK

Before you order

Calculate each elevation by substrate and subtract only large openings; siding profile, rough masonry, spraying, back-rolling, weather, and color change affect coverage.

Worked example

Example: with facade length 40 ft, average paint height 10 ft, unpainted openings 80 sq ft, number of coats 2, the exterior paint calculator returns 3 gal for gallons to buy. The supporting check is quarts equivalent: 9 qt. Replace the prefilled measurements and supplier assumptions with the project values before ordering.

PROJECT GUIDE

Using this calculator well

WHEN TO USE IT

Best use of this calculator

Use the result as a planning estimate, then verify field measurements and product-specific data before ordering or building.

INPUTS EXPLAINED

What each input means

Facade length: Enter the measured value and choose the matching unit (ft, in, yd, m, cm).
Average paint height: Enter the measured value and choose the matching unit (ft, in, yd, m, cm).
Unpainted openings: Enter the project value in sq ft.
Number of coats: Enter the project value used by the calculation.
Coverage per gallon: Enter the project value in sq ft.
Price per gallon: Enter the project value in $.

COMMON MISTAKES

Checks that prevent bad estimates

Mixing units or entering a measurement in a different unit than the selected field unit.
Using a planning default when the exact manufacturer or supplier specification is available.
Rounding intermediate measurements too early instead of rounding the final purchase quantity.
Ignoring waste, compaction, cuts, laps, settlement, or full-package rounding where the project requires them.

SOURCES & REVIEW

How this estimate is supported

The implemented formula, assumptions, and worked example on this page are the calculator-specific reference. BuildYard's broader rules are documented in the Calculation Methodology and Sources & References.

For material density, coverage, yield, dimensions, package quantity, price, and other product-specific values, the current manufacturer or supplier specification should override a planning default.

Last reviewed: September 15, 2026, as part of the site-wide calculator workflow validation pass. See the BuildYard Changelog.

COMMON QUESTIONS

Exterior Paint Calculator FAQ

What does the Exterior Paint Calculator calculate?

It converts the measurements for one façade or rectangular exterior wall surface into the buying units normally used for exterior coating gallons, with the relevant waste, package, weight, or cost outputs shown on the result card.

How accurate is this exterior paint calculator?

The geometry is calculated from the values you enter. Final ordering accuracy still depends on field measurements, supplier density or coverage, product dimensions, compaction, cuts, and the selected allowance.

What should I verify for one façade or rectangular exterior wall surface?

Calculate each elevation by substrate and subtract only large openings; siding profile, rough masonry, spraying, back-rolling, weather, and color change affect coverage. Confirm the selected product, field conditions, and purchasing increments before placing the order.

Should I round the result up?

Yes for indivisible buying units such as bags, sheets, bundles, pallets, boxes, bars, and truck loads. The calculator rounds those purchase quantities up automatically.

KEEP ESTIMATING

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