The question with Emergency Dumpster Rental isn't the size of the container. It's this: Emergency Dumpster Rental is an unplanned container after damage, a failed inspection or a deadline nobody expected, and that's what most people miss going in. Most people find out the hard way that water-damaged material is dense, so the box is sized on weight rather than on the visible heap.
Renting by the yard sets the size. Getting billed by the ton sets the real ceiling, and the two don't move together. If anyone dealing with damage sounds like you, expect to size somewhere in the 20 or 30 yard range — that's where most bookings like yours settle. Know what you're throwing away and how long you need it there — that's the entire booking conversation.
Nobody knows what's actually in a garage or estate cleanout until it's being carried out the door, so the safer order is one size larger than the first guess. Ask what happens to a container that sits mostly empty -- some yards pick up early and adjust the bill, others hold to the full rental period regardless of how much got loaded. Between ordering too big and ordering too small, the safer mistake is still a mistake. Get the estimate right instead.