18.9 litres is equivalent to a 5 US gallon pail, suitable for use on larger jobs. When NatureSecret went looking for a smaller pail geared more for retail use, research showed an average room in an average home required 2.5 gallons of paint (9.5 litres) in order to cover the walls twice. Our pail supplier produces an 11 litre pail that we label as 10 litres, which should be adequate for most average 12'x12' rooms. For some of our colours considered to be more of a highlight colour and in response to customer requests for smaller projects, we have begun to package NatureSecret into a standard 3.78 litre (1 US gallon) can.
The large size, 18.9L is for the larger jobs like exterior projects. Research showed that an average room takes roughly 10L to cover all 4 walls with 2 coats and that is why we have the 10L size. Gallon containers are perfect for one wall coverage, accent colours and small projects. With the variety of sizes available, you should be able to choose the right amount for almost any project without having to worry about batch to batch color variation.