San Mateo is about 522 times smaller than Beijing.

Beijing is approximately 16,411 sq km, while San Mateo is approximately 31 sq km, making San Mateo 0.19% the size of Beijing.
Tip: This to-scale comparison of Beijing vs. San Mateo 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.