Los Angeles is about 1.4 times smaller than Johannesburg.

Johannesburg is approximately 1,644 sq km, while Los Angeles (including the city proper only) is approximately 1,215 sq km, making Los Angeles 73.89% the size of Johannesburg.
Tip: This to-scale comparison of Johannesburg vs. Los Angeles uses the Mercator projection, which distorts the size of regions near the poles.
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