Paint Calculator

Add up all wall areas (perimeter × ceiling height), subtract door and window areas, then divide by the paint coverage rate (typically 350 sq ft per gallon). Multiply by the number of coats. This calculator does all of this automatically.

Most interior wall paints cover 350–400 square feet per gallon. Primer covers 200–300 sq ft/gallon (more porous surface). Exterior paint covers 250–350 sq ft/gallon. High-hide specialty paints may cover 300–350 sq ft/gallon. Check the label on your specific paint for the manufacturer’s stated coverage.

Going from white to another light colour: 1–2 coats. Going from dark to light (e.g. red to white): 3+ coats, sometimes with primer first. New drywall: primer first, then 2 coats. Same colour touch-up: 1 coat. Bold or deep colours: 2 coats minimum for even coverage.

Always paint the ceiling first, then walls, then trim (skirting boards, window frames, doors). This order lets you overlap slightly onto walls when painting the ceiling, then cover those overlaps when you paint the walls, and finally paint trim last for clean edges.

Prime when: painting new drywall, going from a very dark to a light colour, painting over stains or water marks, or painting bare wood/metal. Skip primer when: repainting with the same or similar colour on a previously painted wall in good condition.

Interior paints are formulated for low VOC, washability, and colour retention in controlled environments. Exterior paints contain UV inhibitors, mildewcides, and flexible resins to handle temperature swings, rain, and direct sunlight. Never use interior paint outside — it will peel and fade rapidly.

Completely free. Enter your room dimensions and get your paint quantity estimate in seconds.