Find out exactly how many gallons or litres of paint you need — accounting for doors, windows, ceilings, and multiple coats.
Enter your room's length, width, and wall height, then tell us how many doors and windows it has — standard door and window sizes are automatically deducted from your total paintable area. Choose how many coats you're applying and your paint's coverage rate from the can label to get an exact gallon or litre count.
Most interior paints cover 350–400 square feet per gallon, roughly 8–10 m² per litre, for a single coat on primed drywall. Textured walls, unprimed surfaces, or a big colour change all reduce real-world coverage, so check your specific product label for the most accurate figure.
Ceilings usually call for a flatter, drip-resistant formula, so most painters buy it separately from wall paint. Tick "Include ceiling" above only if you're using the same paint for both surfaces.
Two coats is standard for most colour changes and gives the most even, durable finish. A single coat can work when you're repainting a wall the same or a very similar colour.
Treat a closet or alcove as its own small room using the same calculator, then add the two container totals together — its walls still need covering even though it's a different shape.
Paint is sold in fixed container sizes, and stores typically won't sell partial gallons or litres. Rounding up also leaves a small buffer for drips, spot fixes, and future touch-ups.