Home & Construction

Paint Calculator — Free 2026

Calculate how many gallons of paint you need for any room. Enter dimensions, doors and windows to get an accurate estimate.

Room Length (ft)

Room Width (ft)

Ceiling Height (ft)

Number of Coats

Doors

Windows

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Wall Area (sq ft)

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Paintable Area (sq ft)

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Gallons Needed

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Quarts Needed

How It Works

Enter room dimensions
Add doors and windows
Read your results

How to Estimate Paint for a Room

Estimating paint accurately prevents costly over-buying or frustrating mid-project runs to the store. The calculation is simple: find the total wall area, subtract openings like doors and windows, multiply by the number of coats, and divide by the paint's coverage rate. This calculator uses the industry-standard 350 sq ft per gallon for smooth interior walls.

Wall Area Formula

The perimeter of a rectangular room is calculated as 2 times the length plus 2 times the width. Multiplying the perimeter by the ceiling height gives the total wall area. Standard doors occupy about 20 square feet each and windows about 15 square feet each. Subtracting these deductions gives you the paintable wall area. For precise area measurements of irregular rooms, use our square footage calculator.

Choosing the Right Amount

Most paint projects require two coats for proper coverage and color depth. When changing from a dark color to a light one, plan for three coats or use a tinted primer first. Professional painters recommend buying about 10% more paint than calculated to cover touch-ups, mistakes, and future spot repairs. Leftover paint stored properly can last up to 10 years. Use our unit converter if you need to convert between metric and imperial measurements.

Coverage Variables

The 350 sq ft per gallon estimate assumes smooth, previously painted walls. Textured surfaces like stucco, popcorn ceilings, or bare drywall absorb more paint and reduce coverage to 250-300 sq ft per gallon. High-quality paints with better pigment concentration may cover more area per gallon, while bargain paints may require additional coats to achieve even coverage.

Frequently Asked Questions

How much paint do I need for a room?

Calculate the total wall area by measuring the perimeter of the room and multiplying by the ceiling height. Subtract about 20 sq ft per door and 15 sq ft per window. One gallon covers approximately 350 square feet. Multiply by the number of coats and divide by 350 to get total gallons needed.

How many coats of paint do I need?

Most rooms need 2 coats of paint for even coverage and true color. You may get away with 1 coat if painting a similar color. Dark or bold colors over light walls may require 3 coats. Unpainted drywall always needs a separate primer coat first.

How much wall area does a gallon of paint cover?

One gallon of standard interior latex paint covers approximately 350-400 square feet on smooth walls. Textured or porous surfaces reduce coverage to about 250-300 square feet per gallon. Exterior paint typically covers 250-350 square feet per gallon.

Should I subtract doors and windows from paint area?

Yes. A standard interior door is about 20 square feet and a standard window is about 15 square feet. Subtracting these gives a more accurate estimate and prevents over-buying. However, buy slightly more than calculated for touch-ups and waste.