Boston is about 2.3 times bigger than Manhattan.

Manhattan is approximately 55 km² (21 sq mi), while Boston is approximately 124 sq km, making Boston 127% larger than Manhattan.
Tip: This to-scale comparison of Manhattan vs. Boston 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.