How Much Paint Do I Need for a Room? Complete Guide
Planning a home DIY painting project always starts with one big question. How much paint do you actually need to buy before opening the first can? Buying too little paint leads to mid-project store runs, while buying too much leaves expensive leftover paint cans sitting in your garage for years.
Calculating paint volume is straightforward once you know room surface area and spreading rates. Most standard interior paints cover approximately 350 square feet per gallon on primed walls.
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Step 1: Calculate Total Wall Perimeter & Surface Area
To find gross wall area, measure the perimeter of your room and multiply it by ceiling height.
For example, if your bedroom measures 14 feet long by 12 feet wide with 8-foot ceilings, your calculation looks like this:
- Perimeter: 14 + 12 + 14 + 12 = 52 linear feet
- Gross Wall Area: 52 x 8 = 416 square feet
Step 2: Subtract Doors and Windows
You do not need to paint over glass or wood trim. Professional painters subtract standard allowances for room openings:
- Standard Interior Door: Subtract 21 square feet per door.
- Standard Window: Subtract 15 square feet per window.
Continuing our example room with one door and two windows:
Step 3: Multiply by Number of Coats
Quality interior painting almost always requires two full coats for rich color depth and durability. Multiply your net area by two:
365 sq ft x 2 coats = 730 square feet of total paint coverage needed.
Step 4: Divide by Paint Spreading Rate
Divide your total coverage area by 350 square feet (the standard spreading rate for one gallon of paint):
730 / 350 = 2.08 gallons of paint.
In this scenario, purchasing two 1-gallon cans and one 1-quart can gives you perfect coverage with a small buffer for touch ups. You can test your room dimensions directly in our free Paint Calculator.
