π¨ Paint Calculator
Calculate gallons of paint needed for walls and ceilings.
Paint Needed
How to Use This Calculator
Switch between Room Dimensions mode and Total Area mode. In room mode, enter your room length, width, and ceiling height, then count the doors and windows. The calculator subtracts roughly 20 square feet per door and 15 square feet per window from the paintable wall area. Set your number of coats and the coverage rate for your specific paint.
Measure the room length and width. For an oddly shaped room, break it into rectangles and add the areas together.
Count the doors and windows. Standard interior doors are about 20 square feet. Standard windows run 12 to 15 square feet each.
Set the coverage rate. Most quality interior paints cover 350 to 400 square feet per gallon on smooth surfaces. Drop this to 300 if painting over a dark color or new drywall.
Choose the number of coats. Two coats is standard. Going from a dark color to a much lighter one may need a third coat or a tinted primer coat first.
Paint Coverage Formula
A 12x14 ft room with 8-foot ceilings and two windows plus one door has about 376 square feet of paintable wall. At 350 sq ft per gallon with two coats, that is 2.15 gallons. You would buy 3 gallons to be safe, or 2 gallons plus a quart.
Example Projects
Tips for Your Project
Buy paint in larger containers when possible. A gallon is more economical than four quarts, and a 5-gallon bucket is cheaper per gallon than five individual gallons. If you are painting multiple rooms the same color, box all your gallons together by pouring them into a large bucket and mixing thoroughly. This eliminates batch-to-batch color variation that becomes obvious on your walls under different lighting.
For new drywall, always prime first. New drywall is porous and will absorb your first coat of paint unevenly, leaving a blotchy finish. A quality PVA primer seals the surface in one coat and lets you get full coverage with two coats of finish paint. This actually saves paint overall, even though it adds a step to the process.
Frequently Asked Questions
How much area does one gallon of paint cover?
Standard coverage is 350β400 sq ft per gallon for smooth surfaces. Rough or porous surfaces may need more. Our calculator uses 350 sq ft/gallon as a conservative estimate.
How many coats of paint do I need?
Generally 2 coats for good coverage. Light colors over light: sometimes 1. Dark over light or priming a new surface: 2β3 coats.
Should I account for doors and windows?
Yes β standard doors are ~20 sq ft and windows ~15 sq ft. Subtract these from total wall area for an accurate estimate.
How do I calculate wall area?
Perimeter Γ height gives total wall area. E.g., a 12Γ10 ft room with 8 ft ceilings: (2Γ12 + 2Γ10) Γ 8 = 512 sq ft walls.
What is paint primer?
Primer seals and prepares surfaces for topcoat adhesion. Use primer on new drywall, bare wood, major color changes, or stained surfaces. Primer usually counts as a coat.