How to Calculate Paint Needed
To estimate paint coverage, calculate the total wall area of your room, subtract openings (doors and windows), then divide by the coverage rate of your paint (typically 350 sq ft per gallon). Multiply by the number of coats for your total.
Paint Coverage Formula
Wall Area = 2 x (Length + Width) x Height
Paintable Area = Wall Area - (Doors x 21 sq ft) - (Windows x 15 sq ft)
Gallons Needed = (Paintable Area / 350) x Number of Coats
How to Use This Calculator
- Measure your room length and width in feet
- Measure the wall height (usually 8 feet for standard rooms)
- Count the number of doors and windows
- Select the number of coats (2 is standard)
Tips for Painting Success
- Always use primer on bare surfaces — it improves adhesion and coverage
- Buy all your paint at once to ensure consistent color
- Use a paint calculator like this one to avoid multiple trips to the store
- Invest in quality brushes and rollers for a professional finish
- Paint in the right conditions: 50-85F, low humidity
Paint Calculator FAQ
How much area does a gallon of paint cover?
A gallon of paint typically covers about 350-400 square feet with one coat on a smooth, primed surface. Rough or textured surfaces may require more paint. This calculator uses 350 sq ft per gallon as a conservative estimate.
How many coats of paint do I need?
Most paint jobs require 2 coats for even coverage and durability. You may need 3 coats when painting light over dark colors, using low-quality paint, or painting porous surfaces. One coat may suffice for touch-ups or when using paint-and-primer combos over similar colors.
Should I subtract doors and windows?
Yes. A standard door is about 21 square feet and a standard window is about 15 square feet. Subtracting these areas prevents you from over-purchasing paint. This calculator automatically deducts these areas from the total.
How much paint should I buy extra?
Buy 10-15% more paint than calculated to account for waste, touch-ups, and uneven absorption. Always keep some leftover paint for future touch-ups. This calculator provides both the exact amount and a rounded-up gallon count.
What is the difference between flat, eggshell, and semi-gloss paint?
Flat paint hides imperfections but is hard to clean. Eggshell has a slight sheen and is easy to clean, making it popular for living areas. Semi-gloss is durable and moisture-resistant, ideal for kitchens, bathrooms, and trim. High-gloss is the most durable but shows every imperfection.