Hayward is about 3.5 times smaller than Athens.

Athens (map shows its 34 named neighbourhoods; the area covers the whole city) is approximately 412 sq km, while Hayward (map shows its 16 named neighbourhoods; the area covers the whole city) is approximately 119 sq km, making Hayward 28.8% the size of Athens.
Tip: This to-scale comparison of Athens vs. Hayward 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.