Mammoth Cave National Park is about 1.8 times bigger than Boston.

Boston is approximately 124 sq km, while Mammoth Cave National Park is approximately 219 km² (84 sq mi), making Mammoth Cave National Park 76% larger than Boston.
Tip: This to-scale comparison of Boston vs. Mammoth Cave National Park 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.