Result
3 gallons to buy
After subtracting openings and adding 10% waste, plan for 2.3 gallons.
- Paintable area
- 360 sq ft
- Adjusted coverage area
- 792 sq ft
- Calculated gallons
- 2.3 gal
Measure before estimating
Add the area of each wall, subtract major openings, and enter the number of coats. Fresh drywall and dramatic color changes may need extra paint.
Why waste allowance helps
A small waste factor covers roller loading, touch-ups, rough surfaces, and measurement error.
Formula and assumptions
This calculator uses the inputs above to turn a practical planning question into a usable estimate. The result should be treated as a starting point, because product ratings, room conditions, material waste, and real-world use can vary.
Example calculation
Example inputs: Total wall area: 400 sq ft; Doors and windows: 40 sq ft; Number of coats: 2; Coverage per gallon: 350 sq ft; Waste allowance: 10 %. With those values, the calculator returns 3 gallons to buy. After subtracting openings and adding 10% waste, plan for 2.3 gallons.
Common planning mistakes
Avoid using rough guesses for every input, forgetting waste or safety margin, and treating the estimate as a guaranteed final number. Measure the space, round up when buying materials or equipment, and compare the result with product labels or project instructions.
FAQs
Paint Coverage Calculator questions
Should I subtract trim?
Most quick estimates only subtract large doors and windows. Trim usually does not change the gallon count much.
What coverage number should I use?
Many paints cover roughly 300 to 400 square feet per gallon, but check the can for the exact product.