Trunk comparison: Kia Stonic vs VW Tiguan

Biggest Differences
The most noticeable differences concern the cargo space lengths and the depth of the trunk. The VW Tiguan offers with the seats folded down a cargo space that is 13.8 in or 26% longer and with the first row of seats upright a cargo space that is 7.5 in or 28% longer than the Kia Stonic.
In contrast, the Kia Stonic has a significantly greater trunk depth: +6.7 in or 1700% (loading edge → trunk floor).
Impact on Usability
For transporting long items (e.g., long boxes, furniture parts, long sports equipment like surfboards or skis), the VW Tiguan is clearly more suitable: the longer interior dimensions both with the rear seats up and folded down allow for longer loading without compromises.
Those who often transport longer cargo or regularly need large luggage benefit from the Tiguan solution.
The significantly greater depth of the Kia Stonic means that the trunk floor lies further below the loading edge. Practically, this means: bulky or tall items can be recessed deeper, so the cargo often sits more stably and is less visible (more theft-resistant).
This can be advantageous for bulky but not very long items. At the same time, a significantly deeper trunk can make loading and unloading heavy items somewhat more cumbersome (more bending/reaching), especially if the loading edge height differs only slightly.
The other differences are smaller: the trunk opening of the Stonic is slightly higher (+2 in, about 7%), the width at the narrowest point is minimally larger (+1.6 in, 4%), and the loading edge height is only slightly increased (+1.2 in, 4%).
The width of the trunk opening on the Tiguan is 10% larger, which has a moderately positive effect in practice for very wide cargo but does not reach the threshold of the highlighted differences above.
Conclusion: Those who primarily transport longer items or frequently need maximum cargo length are better served by the VW Tiguan. Those who value a deeper cargo well (stable, "recessed" cargo, less visibility from outside) will find advantages in the Kia Stonic.