How far can a PC with a USB WIFI antenna/adapter be from the router?

[tomworthington2004.tw]

I'm about to buy a USB WIFI adapter/antenna. My router is downstairs and my PC is upstairs. Can the adapter reach that far?

 

[RealBeast]

Upstairs is usually difficult to get great bandwidth (to stream) or great latency (to game). Much depends on the construction materials in your home, surrounding interference, and luck.

You would probably be a lot better with a pair of AV2-1000/1200 powerline adapters. If you still need wireless upstairs, attach either a router configured as an AP or use a powerline AP. HERE is a good site to compare models.