Paint Calculator
Estimate paint for a room.
Input
Result
What is a Paint Calculator?
A Paint Calculator estimates the amount of paint needed to cover the walls, ceiling, or trim of a room. It uses the room dimensions, number of doors and windows, and the paint's coverage rate to calculate how many gallons or liters to buy.
How to calculate paint manually (the formula)
Measure the perimeter of the room and multiply by the wall height: Wall Area = Perimeter × Height. Subtract the area of doors (about 20 sq ft each) and windows (about 15 sq ft each). Divide by the paint coverage (typically 350–400 sq ft per gallon): Gallons = Net Area ÷ Coverage. Multiply by 2 for two coats.
Example calculation
A 12 ft × 14 ft room with 8 ft ceilings has a perimeter of 52 ft. Wall area = 52 × 8 = 416 sq ft. Subtract 1 door (20) and 2 windows (30) = 366 sq ft. At 350 sq ft per gallon: 366 ÷ 350 = 1.05 gallons. For two coats: 2.1 gallons, so buy 2–3 gallons.
Common mistakes
- Not subtracting doors and windows — Painting over doors and windows wastes paint. Measure and subtract their areas for an accurate estimate.
- Forgetting to account for multiple coats — Darker colors or drastic color changes require two or three coats. Always multiply by the number of coats.
- Ignoring paint quality differences — Higher-quality paint often has better coverage (400 sq ft/gal), while budget paint may cover less (250–300 sq ft/gal). Check the label.
Frequently asked questions
How do I calculate how much paint I need?
Divide the total paintable area by the coverage per gallon.
What is the formula for paint coverage?
Gallons needed = Total Wall Area ÷ Coverage per Gallon.
How much area does a gallon of paint cover?
Typically 350–400 square feet per coat.
Should I buy extra paint?
Yes, buy 10% extra for touch-ups and second coats.
Is this free?
Yes, completely free.
Does it work on mobile?
Yes, works on any device.