Trunk comparison: BMW X1 vs Opel Astra Wagon

Key Differences (highlighted: >10%)
The Opel Astra Wagon offers with the front seats upright a trunk that is 6.7 in (19%) longer than the BMW X1. The BMW X1 also has a trunk depth dimension (loading edge → trunk floor) that is 0.4 in (50%) larger and a loading edge that is 4.7 in (20%) higher above the road than the Opel.
The other differences (e.g., trunk length with seats folded +0.8 in/1%, opening height +2.4 in/8%, narrowest width +3.1 in/8%, opening width +0.8 in/2%) are under 10% and practically insignificant.
Impact on Usability
The significantly longer loading area of the Astra with the front seats upright means: with passengers on board, more luggage or longer items can be accommodated in the Astra. For everyday use with a loaded rear seat, the Astra is therefore more practical.
The higher loading edge of the BMW (+4.7 in) has a clear practical consequence: loading heavy or bulky items requires more lifting effort and is less back-friendly. Wheeled luggage can be rolled in less easily than with the lower floor of the Astra.
The larger relative value of the trunk depth measurement in the BMW (0.4 in = 50%) is technically notable but hardly noticeable in practice: a 0.4 in difference hardly changes loading behavior.
With the seats fully folded down, both models are almost equal (only +0.8 in/1% in favor of the Astra), so the maximum cargo capacity with folded seats is practically comparable. The slightly higher opening height of the Astra (+2.4 in) can also make loading tall items somewhat easier but is not a major advantage.
Conclusion
For users who often transport passengers and luggage simultaneously or value easy loading (lower loading edge), the Opel Astra Wagon is the more practical choice.
Those who mainly need maximum loading depth with folded seats will find similar capacity in both models; however, the small depth advantage of the BMW is negligible in practice.