How Much Paint Do You Really Need?
Figuring out how much paint to buy is one of the most common DIY questions. Buy too little and your project stalls mid-project. Buy too much and you are stuck with leftover cans you will never use. Our paint calculator gives you an accurate estimate based on room dimensions, openings, and number of coats.
Paint Coverage Basics
On average, a gallon of paint covers about 350 to 400 square feet in a single coat on smooth walls. Textured surfaces, bare wood, and stucco may need more paint. Our calculator uses 350 sq ft per gallon as a conservative estimate — better to have a little left over than to run out.
The Paint Calculation Formula
- Perimeter = 2 × (Length + Width) — total wall length
- Height = ceiling height
- Openings = doors (≈20 sq ft each) + windows (≈15 sq ft each)
- Coats = number of paint coats (usually 2)
How Many Coats of Paint?
Most interior painting jobs require two coats for a professional, even finish. The first coat provides coverage, the second evens out color and sheen. Some scenarios need even more:
- Light to dark color changes: 2-3 coats
- Dark to light color changes: primer + 2 coats
- New drywall: primer + 2 finish coats
- Same color touch-up: 1 coat may suffice
Example: A 12×10 Bedroom
Room: 12 ft long × 10 ft wide × 8 ft ceiling, 1 door, 2 windows, 2 coats:
- Perimeter: 2 × (12 + 10) = 44 ft
- Wall area: 44 × 8 = 352 sq ft
- Less door + windows: −50 sq ft → 302 sq ft
- Two coats: 604 sq ft total
- Gallons: 604 ÷ 350 = 1.73 gallons → buy 2 gallons
Paint Calculator Tips
- Ceilings add roughly the same area as the floor. Flat ceilings use ceiling paint.
- Trim (doors, baseboards, window frames) — add 0.5-1 gallon depending on room size.
- Textured walls may use 20-30% more paint than smooth walls.
- Primer has similar coverage to finish paint; count it as an additional coat.
FAQ
How much paint do I need for one wall?
Measure wall width × height, divide by 350. A typical 12×8 wall needs roughly 0.3 gallons per coat.
Should I buy a 5-gallon bucket?
If you need more than 3-4 gallons, a 5-gallon bucket is usually more economical per gallon.
How long does paint last in the can?
Unopened latex paint lasts 2-10 years. Opened and properly sealed, 2-5 years.