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Calculation Machine

Paint Calculator

Gallons needed for walls, doors and windows deducted.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Paint needed
2.42 gallons
Buy
3 gallons
Paintable wall area
453 sq ft
Primer if bare drywall
1.51 gallons

Quick answer

One US gallon of paint covers about 350–400 square feet per coat on primed drywall.

The formula

Gallons = wall area × coats ÷ 375

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Room perimeter60 ft
  • Wall height9 ft
  • Doors2
  • Windows3
  • Coats2

Result

  • Paint needed2.42 gallons
  • Buy3 gallons
  • Paintable wall area453 sq ft
  • Primer if bare drywall1.51 gallons

How to use the Paint Calculator

  1. 1Measure the perimeter of the room.
  2. 2Enter the wall height and openings.
  3. 3Choose how many coats you plan to apply.

Frequently asked questions

How much does a gallon cover?

About 375 sq ft per coat on smooth primed walls; textured or porous surfaces can drop to 250 sq ft.

Do I need primer?

Yes on bare drywall, over strong colour changes and on stained or patched areas — otherwise a self-priming paint is fine.

About this calculator