Buying too much paint wastes money. Buying too little means a mid-project hardware run and the risk of a slightly different dye lot on your second can. Getting the estimate right is simpler than most people think — here's exactly…
Buying too much paint wastes money. Buying too little means a mid-project hardware run and the risk of a slightly different dye lot on your second can. Getting the estimate right is simpler than most people think — here’s exactly how to calculate how much paint you need.
The Basic Paint Calculation Formula
Start with the paintable wall area: add up the perimeter of your room (all four walls combined) and multiply by the ceiling height. Then subtract the area of doors (about 21 sq ft each) and windows (about 15 sq ft each). Divide the remaining area by the coverage rate on your paint can — typically 350–400 square feet per gallon for one coat.
Use our free paint calculator to do this automatically for any room size.
Example Calculation
A standard 12 × 14 bedroom with 9-foot ceilings, one door, and two windows:
- Perimeter: (12 + 14) × 2 = 52 linear feet
- Wall area: 52 × 9 = 468 sq ft
- Subtract openings: 468 – 21 – 30 = 417 sq ft
- At 350 sq ft/gallon: 417 ÷ 350 = 1.19 gallons per coat
- For 2 coats: 1.19 × 2 = 2.38 gallons — buy 2.5 or 3 gallons
How Many Coats Do You Need?
Two coats is standard for most painting projects. You may need three coats when making a dramatic color change (dark to light or light to dark), painting over a glossy surface, or using a light paint over a stained or patchy wall. One coat may suffice if you’re touching up with the same color.
Primer: When to Use It
Prime before painting new drywall (it would otherwise absorb paint unevenly), when making dramatic color changes, when painting over glossy surfaces, or when covering stains. A coat of primer can reduce the total paint coats needed from 3 to 2, saving money overall.
Understanding Paint Coverage Rates
Paint cans list coverage rates assuming ideal conditions: smooth surface, correct application technique, and no thinning. Real-world coverage is typically 10–15% less. Textured walls (popcorn, knockdown, or heavy texture) absorb significantly more paint and may require 30–40% more coverage to account for the extra surface area.
Choosing the Right Finish
- Flat/Matte: Ceilings and low-traffic bedrooms — hides imperfections best
- Eggshell: Living rooms and bedrooms — easy to clean, some sheen
- Satin: Hallways, bathrooms, kitchens — durable and washable
- Semi-gloss: Trim, cabinets, doors — high durability and moisture resistance
- High-gloss: Cabinets, furniture — most durable, shows every imperfection
Conclusion
Calculating paint needs accurately is a five-minute exercise that pays off in time and money. Measure your walls, subtract your openings, account for your chosen number of coats, and always buy a bit extra for touch-ups. Properly stored paint stays good for years in a sealed can — a spare quart for touch-ups is always worthwhile.