Trunk comparison: Citroen C3 vs Tesla Model 3

The Tesla Model 3 offers significantly more cargo space lengthwise: it has +20.1 in (38%) more trunk length with the seats folded down and +15.7 in (60%) more when the front row is upright. The width of the Tesla's trunk opening is also +4.7 in (14%) larger than that of the Citroën.
In contrast, the Citroën C3 has a significantly higher trunk opening (+10.6 in / 52%), a deeper trunk well between the loading edge and floor (+4.7 in / 109%), and a higher loading lip above the road (+4.3 in / 16%). The narrowest trunk width differs by only +0.4 in (1%) in favor of the C3, which is negligible.
Impact on Usability
For long items and large cargo volumes (e.g., long slats, furniture parts, many suitcases), the Tesla Model 3 is clearly advantageous: the significantly greater loading length and wider opening make it easier to load long or bulky items, and the lower loading lip makes lifting heavy loads easier.
However, the lower opening height and shallower well of the Tesla limit loading very tall items; such items usually need to be transported tilted or lying down.
The Citroën C3 is better suited for tall or upright cargo (e.g., boxes, strollers, tall furniture parts): the higher opening and deeper well provide more vertical space.
A disadvantage is the higher loading lip, which makes lifting heavy items more strenuous, as well as the shorter loading length, which limits transporting long items. For wide, flat items, the somewhat narrower opening of the C3 offers less convenience than the Tesla.
In short: Tesla Model 3 = better for long and wide cargo as well as easier loading and unloading of heavy loads; Citroën C3 = better for tall, upright, and stacked cargo, but with higher lifting and loading effort.