Nantucket is around the same size as San Francisco.

San Francisco (including the city proper only) is approximately 121 sq km, while Nantucket is approximately 124 km² (48 sq mi), making Nantucket 2% larger than San Francisco.
Tip: This to-scale comparison of San Francisco vs. Nantucket 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.