The short version on Whole Home Cleanout: it is every room emptied in one go, usually ahead of a sale or a move. You'll want this settled before the truck shows up: you will run out of room long before you run out of tonnage on a domestic clearance.
Two ceilings apply to every load: how much fits, and how much is allowed to weigh. Dirt and concrete hit the second one first; furniture and boxes usually hit the first. When sellers and executors call in this kind of job, the debris volume is usually easy to anticipate in advance, so the containers that get dispatched tend to land in the 20 or 30 or 40 yard bracket. Two things shorten this call: how many days you'll need the container, and whether anything in the load is restricted.
Couches, mattresses and cardboard fill a container fast by size alone, while the scale barely notices they're in there. Find out if a locking lid or gate is available for a container that will sit on the property overnight in a neighborhood with foot traffic. Ordering slightly larger than you think you need costs less trouble than a second pickup for the overflow, so when in doubt, size up rather than risk a return trip.