Trunk comparison: BMW 5 Series Touring vs Kia Sportage

Key Differences
The BMW 5 Series Touring offers significantly more cargo length: with the seats folded down, the trunk is +8.3 in (12%) longer than the Kia Sportage and with the first row of seats upright, +7.5 in (21%) longer.
All other measurements differ only slightly: trunk depth is the same, the Kia's trunk opening is +1.2 in (4%) higher, the Kia's loading edge is +2.4 in (9%) higher, the narrowest width in the trunk is +1.2 in (3%) larger in the BMW, and the opening width in the BMW is +0.4 in (1%).
Impact on Usability
The significantly greater cargo length of the BMW makes it more practical for long items and increased cargo volume with seats folded down – useful for furniture, long sports equipment, or regular transport of bulky goods.
Even with the normal seat configuration, the BMW offers +7.5 in (21%) more usable length for longer loads behind the seats.
The Kia scores with a slightly higher trunk opening (+1.2 in), which minimally eases loading very tall items, and a higher loading edge (+2.4 in), which, however, makes lifting heavy loads somewhat more strenuous.
Overall, width and depth are similar enough that the side usable space and floor area are comparable for both models.
In short: For frequent transport of long or bulky items, the BMW 5 Series Touring is the better choice.
Those who benefit from a somewhat higher opening and higher ground clearance (easier loading of tall items, slightly more underbody clearance) can consider the Kia Sportage — but the differences there are smaller and less influential than the length advantages of the BMW.