How do I calculate paint for a room?
Wall area = 2 × ceiling height × (length + width). Add ceiling area (length × width) if you are painting the ceiling. Divide total coverage by sq ft per gallon on your paint can.
Room Paint Calculator
A rectangular room is the most common DIY paint job. Enter length, width, and ceiling height in feet and inches — we calculate wall area, optional ceiling, door and window deductions, then gallons to buy.
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Default 10% for touch-ups
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How wall area is calculated
Wall square footage = 2 × ceiling height × (length + width). That is the perimeter multiplied by height — the standard method paint stores and contractors use for estimates.
Toggle ceiling paint separately if you are doing walls only. Standard deductions: about 20 sq ft per door and 15 sq ft per window. Adjust openings in project settings if your home differs.
Multi-room projects
Add up to five rooms and the calculator totals paintable area and gallons for the whole job — useful when painting a hallway plus bedrooms in one colour.
For accent walls or different colours per room, run separate estimates or use our accent wall wallpaper calculator if one wall is wallpaper instead of paint.
Before you roll — prep checklist
Gallon counts assume clean, sound surfaces. Peeling paint, patched holes, and glossy old paint change how much product you use. See how to prep walls for painting and wall repair before painting before you buy materials.
Related guides
Frequently asked questions
How many coats should I plan for?
Most interior walls need two coats over primer or a color change. Primer alone is often one coat. Adjust the coat count in project settings.
Should I subtract doors and windows?
Yes for a closer estimate. A standard door is about 20 sq ft and a window about 15 sq ft. The calculator deducts these automatically.
Related calculators
Paint Calculator · https://paint-calculator.ca/room-paint-calculator/