Received Signal Strength Indicator (RSSI) is an estimated measurement of how well a device can hear, detect and receive signals from any wireless access point or Wi-Fi router.
An RSSI closer to 0 is stronger, and closer to –100 is weaker.
For best performance, you want your RSSI to be as high as possible. A useful rule of thumb is that if the RSSI is less than –70 dBm, you are unlikely to have good performance over Wi-Fi for bandwidth intensive tasks.
WifiInfoView is a free application for Windows which can, among other measurements, display the RSSI of all networks detected by your computer.
Installation and Use of WifiInfoView:
Optional: Compare the RSSIs for all networks in range of your device
iwconfig