Trunk comparison: BMW 5 Series Touring vs BMW X1

Key Differences
The BMW 5 Series Touring offers significantly more cargo length: with the seats folded down, the trunk is 10.2 in (16%) longer and with the first row of seats upright, 7.5 in (21%) longer than the BMW X1. The BMW X1 has a noticeably greater trunk depth (loading edge to trunk floor): it is 1.2 in (200%) higher than in the 5 Series Touring.
All other differences (trunk opening height +0.8 in/3%, loading edge height +2 in/8%, narrowest width +2.4 in/6%, opening width +0.4 in/1%) are small and under 10%.
Impact on Usability
The greater cargo length of the 5 Series Touring makes it better suited for long items such as skis, long furniture parts, or mattresses and for a flatter, longer cargo floor with the seats folded down. Those who regularly transport long or bulky items have significantly more flexibility with the 5 Series.
The greater depth in the X1 means that the storage space from the loading edge to the floor is deeper — practical for storing items protected below the loading edge or to better utilize volume in depth.
However, this comes with a slightly higher loading edge (about 2 in), which makes lifting heavy items somewhat less convenient. The slightly higher opening (+0.8 in) minimally facilitates loading very tall individual pieces through.
The slightly greater narrowest width in the 5 Series (about 2.4 in) helps to accommodate wider items more easily but is not a major advantage over the X1. Overall: for length and a flat, large cargo volume, the 5 Series Touring is the better choice; for deeper storage volume and somewhat more compact exterior dimensions, the X1 can be more practical if the slightly higher loading edge is acceptable.