Paint Calculator
A paint calculator estimates how many liters or gallons of paint — and how many cans — you need to cover a room, based on wall dimensions, the number of doors and windows, and the number of coats. Buying the right amount matters: too little means an extra trip to the store and possible color-batch differences, while too much wastes money and leaves leftover paint to store or dispose of. Entering accurate measurements turns guesswork into a precise shopping list.
The calculation starts from the paintable area: the perimeter of the room multiplied by wall height, minus the area occupied by doors (about 1.6 m² each) and windows (about 1.2 m² each, varying by size). That area is then divided by the paint's coverage rate — commonly 10 to 12 m² per liter per coat for standard interior latex, though porous or unpainted surfaces absorb more. Multiplying by two or three coats and rounding up to whole cans gives a realistic purchase quantity for any painting project.
How it works
Paintable Area = (2 × (Length + Width) × Height) − Door Areas − Window Areas. Liters Needed = (Paintable Area × Number of Coats) ÷ Coverage Rate, where typical interior latex covers about 10-12 m² per liter per coat (roughly 350-400 sq ft per US gallon). Example: a 4 × 3 m room with 2.6 m ceilings has 36.4 m² of wall; subtracting one door (1.6 m²) and one window (1.2 m²) leaves 33.6 m². Two coats at 11 m²/L require 33.6 × 2 ÷ 11 ≈ 6.1 L, so buy two 3.6 L cans or one 5 L plus touch-up.
Use cases
- Estimating how many cans of paint to buy before repainting a bedroom or living room
- Comparing the real cost of paints with different coverage rates and can sizes
- Planning paint quantities for a whole apartment or house renovation, room by room
- Calculating extra paint needed for a second or third coat on a color change
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12 × 12 ft room with 8 ft ceilings has about 384 sq ft of wall area. After subtracting a door and a window (roughly 35 sq ft), around 350 sq ft remain. At a typical coverage of 350-400 sq ft per gallon, you need about 1 gallon per coat, so 2 gallons for two coats.
How many square meters does 1 liter of paint cover?
Standard interior latex paint covers approximately 10 to 12 m² per liter per coat on a sealed, previously painted surface. Coverage drops on porous, textured, or unpainted walls, which absorb more paint, and premium paints with higher solids can cover slightly more. Always check the manufacturer's stated coverage on the can.
Do I need one or two coats of paint?
Two coats are the standard recommendation for uniform color and durability, especially when changing colors. One coat may suffice when repainting with the same or a very similar color on a well-prepared surface. Covering a dark color with a light one, or painting bare drywall, can require a primer plus two or even three coats.
Should I subtract doors and windows when calculating paint?
Yes. A standard door occupies about 1.6 m² (21 sq ft) and a typical window about 1.2 m² (15 sq ft), and that area receives no wall paint. In rooms with several openings the difference can be a full liter or more, so subtracting them keeps the estimate accurate and avoids buying excess paint.
How much extra paint should I buy for touch-ups?
A common rule is to add about 10% to the calculated amount, or simply round up to the next full can. Keeping some leftover paint from the same batch is useful for future touch-ups, since different production batches of the same color can show slight tone variations.