Vienna is about 30 times bigger than Cocos (Keeling) Islands.

Cocos (Keeling) Islands is approximately 14 sq km, while Vienna is approximately 415 sq km, making Vienna 2,863% larger than Cocos (Keeling) Islands.
Tip: This to-scale comparison of Cocos (Keeling) Islands vs. Vienna uses the Mercator projection, which distorts the size of regions near the poles.