Paint Quantity Estimator

How this tool works

The estimator sums the area of each wall (width × height), subtracts the area of doors and windows, multiplies by the number of coats, divides by coverage per gallon, and adds an allowance for the surface condition and color change.

Example: A 12 ft × 15 ft room with 8 ft walls, one standard door, and two standard windows has about 381 sq ft of paintable area. Two coats at 350 sq ft per gallon plus a 10% allowance rounds to about 3 gallons.

Assumptions used

• Standard door area used when not customized: 21 sq ft (approximately 3 ft × 7 ft).
• Standard window area used when not customized: 15 sq ft (approximately 3 ft × 5 ft).
• Coverage per gallon is based on the manufacturer's label — typical latex paint covers about 350 sq ft per gallon on smooth surfaces.
• Primer, if needed, is estimated separately and is not included in the final gallon count.

Practical tips

• Always check the paint can's label for coverage — it varies by product and finish.
• Buy paint in a single batch to reduce color variation between cans.
• Save any leftover paint (labeled) for future touch-ups.
• For dramatic color changes or over unfinished surfaces, expect to add a primer coat.

Frequently asked questions