Paint Needed
Estimate how many gallons of paint you need for room walls.
About Paint Needed
Rooms are painted over their wall perimeter times the wall height, with door and window openings subtracted. Multiplied by the number of coats and divided by the coverage of one gallon, this gives the gallons to buy. Painting uses roughly one coat to an even primer before asking your color of coverage, and buying the right amount avoids both waste and a second trip to the store.
Formula
Paint Needed
Gallons = (perimeter x wall height - openings) x coats / coverage
- perimeter
- Total length of the walls
Worked example
With the default values below, Paint Needed returns Gallons Needed of 3. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Room width
- 12 ft
- Room length
- 14 ft
- Wall height
- 8 ft
- Door openings
- 21 sq ft
- Window openings
- 15 sq ft
- Coatsminimum 1
- 2
- Coverageminimum 1 sq ft/gal
- 350 sq ft/gal
Results
- Wall Area
- 380 sq ft
- Total Area to Paint
- 760 sq ft
- Gallons Needed
- 3 gal
Step by step
- 1Values used
- 2Paint Needed
- 3Gallons Needed= 3 gal
- 4Wall Area= 380 sq ft
- 5Total Area to Paint= 760 sq ft
Assumptions and limits
- The result is derived only from the 7 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Paint Needed calculated?
Gallons = (perimeter x wall height - openings) x coats / coverage Rooms are painted over their wall perimeter times the wall height, with door and window openings subtracted. Multiplied by the number of coats and divided by the coverage of one gallon, this gives the gallons to buy.
Why does Paint Needed matter?
Painting uses roughly one coat to an even primer before asking your color of coverage, and buying the right amount avoids both waste and a second trip to the store.
What values do I need to enter?
This calculator takes 7 inputs: Room width, Room length, Wall height, Door openings, Window openings, Coats, Coverage. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.