diff --git a/goto_cloud/migration_commander/device_identification.py b/goto_cloud/migration_commander/device_identification.py
index 41949f5..9950975 100644
--- a/goto_cloud/migration_commander/device_identification.py
+++ b/goto_cloud/migration_commander/device_identification.py
@@ -55,8 +55,8 @@ def _map_unallocated_devices_onto_source_devices(self, unallocated_devices):
                 matching_device_id = next(
                     (
                         target_device_id
-                        for target_device_id, target_device
-                        in unallocated_devices.items() if target_device['size'] == source_device['size']
+                        for target_device_id, target_device in unallocated_devices.items()
+                        if round(target_device['size'] / 1024 ** 3) == round(source_device['size'] / 1024 ** 3)
                     ),
                     None
                 )