How to Calculate Paint Quantity
Running out of paint mid-project is one of the most frustrating DIY experiences. Buying too much wastes money and creates disposal problems. A quick calculation before heading to the store saves time and money.
The formula is simple: (Net area × number of coats) ÷ coverage rate = gallons needed. Add 10% for waste, drips, and touch-ups. For a standard room (12×12 ft with 8-ft ceilings), you'll need roughly 1.5–2 gallons for two coats.
To measure your walls: add up the perimeter of the room (in feet), multiply by ceiling height, and subtract 20 sq ft per door and 15 sq ft per window. For ceilings, just multiply length × width.
Frequently Asked Questions
Primer is separate from paint and has its own coverage rate (typically 300–350 sq ft/gal). It's essential for bare drywall, drastic color changes, or stain-blocking. Using primer first often reduces the number of paint coats needed from 3 to 2.
Keep at least one quart of leftover paint for touch-ups. Color matching years later is difficult, especially as paint ages. Label the can with the room name and paint color code for easy reference.
Flat/matte hides imperfections best; use for ceilings and low-traffic walls. Eggshell/satin is wipeable and ideal for living rooms and bedrooms. Semi-gloss is moisture-resistant and best for kitchens, bathrooms, and trim.