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Paint Calculator
Calculate how many gallons of paint to buy for any room. Enter wall area, number of coats, and deduct doors and windows — results are rounded up so you never run short.
About This Calculator
Enter your wall area, number of coats, and subtract doors and windows to get an accurate paint estimate. Results are always rounded up to the nearest whole gallon so you never run short mid-project.
How It Works
Net wall area = total wall area minus door and window deductions (~20 sq ft per door, ~15 sq ft per window). Gallons needed = net area × coats ÷ coverage rate. Gallons to buy = ⌈gallons needed⌉ (always rounded up).
The Formula
gallons = (netArea × coats) ÷ coverage buy = ⌈gallons⌉
- netArea
- wall area after door/window deductions (sq ft)
- coats
- number of paint coats
- coverage
- sq ft per gallon (default 350)
Frequently Asked Questions
- How do I measure wall area?
- Measure the perimeter of the room (sum of all wall lengths) and multiply by the ceiling height. For example, a 12×14 ft room with 9 ft ceilings has (12+14+12+14) × 9 = 468 sq ft of wall area before deductions.
- Why does the calculator round up?
- Running out of paint mid-project means a visible color mismatch when you buy a second batch. Rounding up ensures you have enough, and leftover paint is useful for touch-ups.
- What coverage rate should I use?
- The default 350 sq ft/gallon is a conservative standard for latex interior paint. Many paints cover 400 sq ft/gallon — check your paint can label and enter that number for a more accurate estimate.
Estimates only. Coverage figures (sq ft/gallon, bag yield, BTU/sq ft) are industry rules of thumb with real-world variance. Verify quantities with your supplier before purchasing.