Oahu is about 11 times smaller than Hawaii.

Hawaii is approximately 16,635 sq km, while Oahu is approximately 1,545 km² (597 sq mi), making Oahu 9.29% the size of Hawaii.
Tip: This to-scale comparison of Hawaii vs. Oahu uses the Mercator projection, which distorts the size of regions near the poles.
Our free app, MapSize by MyLifeElsewhere — compare any two places, to scale on your mobile device.