Three things decide whether a container works: how much it holds, how much floor space it takes, and whether one person can move it when full. The number printed on the side answers only the first.
Picking a container is the first decision of any cleanout and the one that costs twice when it goes wrong. Order something too small and the hauler returns for a second load. Order something too large and you pay to move air. The trap is that the number on the container describes volume only, while the invoice is often settled by weight.
Most homes have a forgotten gas can somewhere: fuel left over from last summer’s mowing, a can bought for a generator that never ran, or a tank in a car, boat, or motorcycle unused for months. Sooner or later, the question arises of how to dispose of old gasoline without creating a fire hazard or polluting the ground.
A 20 yd dumpster is the middle size in most roll-off fleets. It is large enough for a kitchen remodel, a roof tear-off on a modest house, or a full garage cleanout but small enough to fit in a standard residential driveway. That balance is why many homeowners and contractors start their search with this size.