You came here for Estate Cleanout Dumpster Rental. What you need to know first is that it is clearing a family property to a legal timetable, at a pace set by people rather than machinery. There's a single variable that moves this more than the rest combined: appraisal and donation belong before disposal, because nothing comes back out of the container.
What you see is cubic yards. What you pay for past the limit is tons. Dense material closes that gap fast. You're likely executors and families if you're reading this, and the sizing question for that group usually lands within 20 or 30 yards. The booking is short once you know the weight of the load and the length of time you need the container on-site.
Furniture and mattresses take up space without much weight behind them, so the container runs out of room long before it comes close to its hauling limit. Ask whether loading labor is included, since most rentals are just the container -- filling it is on the renter unless a labor add-on is arranged separately. You're not choosing a size so much as choosing how much you trust your own estimate of the load.