Saint Petersburg is about 16 times smaller than Moscow.

Moscow (map shows its 125 districts within the pre-2012 boundary; the area includes New Moscow) is approximately 2,562 sq km, while Saint Petersburg is approximately 160 sq km, making Saint Petersburg 6.25% the size of Moscow.
Tip: This to-scale comparison of Moscow vs. Saint Petersburg uses the Mercator projection, which distorts the size of regions near the poles.
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