That's an excellent and practical question! When comparing the capacity of round and rectangular waste bins, the shape itself is the key factor, not necessarily a simple "which holds more." It primarily comes down to how efficiently they use the space they occupy.
Imagine you have a designated corner or a spot against a wall. A rectangular bin can fit snugly into that corner, utilizing almost 100% of its footprint for volume. Its straight sides allow it to fill the available space completely. A round bin, on the other hand, will always have gaps in the corners when placed in a right-angled space. This means for the same floor area, a rectangular bin typically offers greater usable capacity.
However, capacity isn't just about maximum volume. A round bin's advantage is its accessibility. There are no corners for trash to get stuck in, making it easier to line with bags and to clean. The circular shape also distributes pressure evenly, which can be beneficial for certain materials.
In summary: if your priority is maximizing volume for a given floor space (like in a tight kitchen corner or a utility room), a rectangular bin is generally more efficient and holds more. If ease of use, cleaning, and flexible placement are your main concerns, a round bin is often the more practical choice, even if its theoretical capacity for its footprint is slightly less.
For similar external dimensions, a rectangular bin will almost always have a higher listed capacity in liters or gallons. But always check the actual volume specification when purchasing, as the shape alone doesn't tell the whole story!