Most small, self-contained appliance composters were designed for seasonal use only. When a manufacturer states that a model should be used only for seasonal or cottage use, then the number of users listed is usually for 20 to 60 days out of a 365-day year. Manufacturers of seasonal systems usually list a much smaller number of users for residential (365-day) use.

European manufacturers use the person-day (PE) approach (one person over 24 hours). For example, a toilet with 600 person days of capacity means one person could use the system for 600 days or four people, 150 days.

Some composters sized for public facilities are rated by uses per year, as many public facilities measure usage this way. The problem: The usage of a public facility can vary widely; parks have found that systems rated for 3000 uses per year cannot manage when 2000 of the park’s uses can occur in two months!