Hello Party Favorz,
I would expect a single Google WiFi unit to cover an apartment that size well enough. If there are a lot of interior walls made with solid construction materials (concrete, brick, plaster, etc.), you may still have coverage challenges, but if you can manage to place the unit as close to the center of the apartment as possible, it should still perform well enough.
Do be aware that WiFi doesn't typically deliver 1Gbps throughput. The explanation gets technical fairly quickly, but the short version is that it's limited by the combination of what the device itself is capable of and what the WiFi access point is capable of. Google WiFi is an AC1200 2x2 access point, so it will be limited to 866Mbps over 5GHz. But, that's only possible over relatively short ranges, doesn't account for the substantial overhead inherent to WiFi, and assumes the device it's talking to has at least an AC1200 2x2 radio as well (many devices don't). WiFi is a great convenience technology. But, if you want to really go fast, use Ethernet.
-From MichaelP, Gold Product Expert.
