Melbourne is about 2.5 times bigger than London.

London (including the 32 boroughs of greater London) is approximately 1,572 sq km, while Melbourne (the 27 councils of metropolitan Melbourne, without the Yarra Ranges, Cardinia, Mornington Peninsula and Nillumbik) is approximately 3,915 sq km, making Melbourne 149% larger than London.
Tip: This to-scale comparison of London vs. Melbourne uses the Mercator projection, which distorts the size of regions near the poles.
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