Boston is about 27 times smaller than Hanoi.

Hanoi is approximately 3,360 sq km, while Boston is approximately 124 sq km, making Boston 3.69% the size of Hanoi.
Tip: This to-scale comparison of Hanoi 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.