Oahu is about 1.2 times smaller than Maui.

Maui is approximately 1,883 km² (727 sq mi), while Oahu is approximately 1,545 km² (597 sq mi), making Oahu 82.05% the size of Maui.
Tip: This to-scale comparison of Maui 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.