Here's the distinction that matters for Same-Day Dumpster Rental: it is an immediate drop, subject to whether a truck happens to have a gap. Ask about this specifically, because it rarely comes up unless you raise it: availability collapses after storms and at month end, when every hauler is already committed.
A box of old carpet and a box of broken tile can be the same size and still hit completely different limits. One runs out of room, the other runs out of allowance. The booking pattern here skews toward anyone on a compressed timeline, since the job produces a fairly predictable volume of debris, which is why 10 or 20 yard containers cover most of what actually gets ordered. Skip the back-and-forth by knowing two things up front: clearance for delivery, and whether the container will sit on the street or the driveway.
This category has no single rule. Some loads run out of room, others run out of weight allowance, and which one hits first depends on what actually goes in. Ask what the cancellation window looks like if the delivery date needs to move. Some yards charge nothing with a day's notice, others charge a restocking fee. Don't split the difference between two sizes. Pick the one that covers the heavier estimate, because running short means a second delivery, not a partial refill.