Paint Calculator

Estimate how much paint you need for walls and ceilings, account for doors and windows, choose the number of coats, and convert the result between gallons and litres.

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Use your paint can's coverage when availableCoverage varies by product, surface, texture and application method. The default coverage is a planning estimate; use the manufacturer's label or technical data for a product-specific result. Sherwin-Williams notes that coverage is commonly around 350–400 sq ft per gallon, while actual requirements vary. citeturn818140search0turn818140search1

Calculate Paint Needed

Enter room dimensions in your chosen unit system. Add additional rooms or spaces when needed.

Adjust this to the coverage shown on your paint product. Default: 375 sq ft/gal.
A small allowance can cover touch-ups and field losses; it is optional.

Rooms / spaces

How to use the Paint Calculator

  1. Choose Imperial or Metric units.
  2. Enter each room's length, width and wall height.
  3. Subtract doors and windows; ceiling area can be included when needed.
  4. Set the number of coats and replace the default coverage with the coverage printed on your paint product.
  5. Calculate and use the result as a planning estimate, then round to the available container sizes.

What the calculation includes

  • Four wall surfaces for each room.
  • Optional ceiling area.
  • Doors and windows deducted from paintable area.
  • Multiple rooms combined into one estimate.

Paint coverage matters

There is no universal coverage number for every paint. Sherwin-Williams says a gallon typically covers about 350–400 square feet, but surface texture, application method and the product itself can change requirements. citeturn818140search0turn818140search1

Simple formula

Wall area = 2 × (length + width) × wall height
Paintable area = wall area + ceiling (optional) − openings
Coat area = paintable area × coats
Paint = coat area ÷ coverage × (1 + overage)

Frequently Asked Questions

How much paint does one gallon cover?

Sherwin-Williams says a gallon of paint typically covers about 350–400 square feet, but product, surface condition and application method can change the actual amount needed. Check the product label or technical data for the paint you are using. citeturn818140search0turn818140search1

Should I subtract doors and windows?

Yes. Deducting significant openings gives a closer estimate of the actual paintable surface. Small openings and trim can be handled differently depending on the project.

Do two coats double the paint?

As a planning calculation, two coats are treated as twice the coated area. Actual product requirements can differ because hiding, substrate condition and application technique affect coverage.

Should I add extra paint?

A modest planning allowance can help with touch-ups and measurement uncertainty, but the appropriate amount depends on the project. Product-specific guidance should take priority.

Can I use litres instead of gallons?

Yes. The calculator supports metric dimensions and litre-based coverage as well as imperial dimensions and square-feet-per-gallon coverage.