Paint Calculator: Square Feet

This paint calculator works in square feet using the same method a painting contractor uses to quote a room. First, it finds your total wall area with 2 × (Length + Width) × Height, which accounts for all four walls of a rectangular room. It then subtracts a standard allowance for each door (21 sq ft, based on a typical 3 ft × 7 ft door) and each window (15 sq ft, based on a typical 4 ft × 3.75 ft window), since you do not paint over these openings.

Once the paintable area is known, the calculator divides it by your chosen paint's coverage rate per litre, then multiplies by the number of coats you select. Coverage rate depends on paint quality: economy emulsions typically cover around 110 sq ft per litre per coat, premium emulsions around 130 sq ft, and luxury washable emulsions up to 140 sq ft, because better paints carry more pigment and binder per litre and need less product to achieve full, even coverage.

The litres required are then rounded up and matched against standard paint can sizes (20L, 10L, 4L and 1L) to suggest the most practical combination to buy, for example "1 × 10L + 1 × 4L" instead of just telling you to buy "11.3 litres", which is not something you can actually purchase. Buying slightly more than the exact number is normal practice to account for touch-ups and uneven absorption, especially on a freshly plastered wall.

If you toggle on "Include Ceiling", we add your room's floor area (Length × Width) to the paintable area, since ceilings are usually painted in a single coat of white or a lighter shade using the same litre-per-area method. If you toggle on "Include Putty & Labour Charges", we add a standard labour and wall-putty rate per square foot on top of material cost, reflecting typical painter charges for surface preparation, putty application and painting across two coats.

Tip: always buy slightly more paint than the calculator suggests (round up to the next full can) rather than slightly less. Matching a paint shade exactly from a second, separately-mixed batch partway through a room is far harder than it sounds, even with the same shade code.