Barcelona is about 1.4 times smaller than Dayton.

Dayton is approximately 145 sq km, while Barcelona is approximately 101 sq km, making Barcelona 70.08% the size of Dayton.
Tip: This to-scale comparison of Dayton vs. Barcelona 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.