Trunk comparison: Audi A3 Sportback vs Audi Q5

Key Differences
There are four relevant differences in the cargo space: The Audi Q5 is longer in loading volume — +6.7 in (11%) when all seats are folded down and +7.1 in (23%) with the first row upright — additionally, the Q5's opening is significantly wider by +6.3 in (16%).
In contrast, the A3 Sportback has a significantly deeper cargo well (distance from loading edge to trunk floor) by +3.1 in (100%) compared to the Q5.
Implications for Usability
The longer loading surfaces and wider opening of the Q5 make it more practical for long or wide items (skis, slats, furniture parts, bulky sports equipment) and facilitate loading bulky parts because more length and a larger opening width are available.
The Q5 is therefore better suited for users with regularly large or bulky cargo needs.
The deeper cargo well of the A3 means that cargo sits lower inside, creating partially more usable volume in the lower area; small items can be stored better and sit lower in the vehicle (lower center of gravity).
For everyday use — shopping bags, luggage for short trips, or loosely stored luggage — this can be advantageous. However, the opening is narrower and the loading length shorter, making very long or wide items less suitable.
Additionally relevant: The loading edge of the Q5 is 2.8 in higher above the road, which makes lifting heavy items in somewhat more demanding; this difference is 10% and noticeable but smaller than the differences highlighted above.
In summary: Those who frequently transport long or wide loads benefit from the Q5. Those who mainly prefer everyday, low-lying cargo and a lower loading position will find the A3 more practical.