Oahu is about 1.3 times bigger than Los Angeles.

Los Angeles (including the city proper only) is approximately 1,215 sq km, while Oahu is approximately 1,545 km² (597 sq mi), making Oahu 27% larger than Los Angeles.
Tip: This to-scale comparison of Los Angeles vs. Oahu uses the Mercator projection, which distorts the size of regions near the poles.
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