Also available on Windows
NetSpot is a wireless signal assessment and site survey application for Mac. It provides two ways of measuring your WLAN signal strength. The first – and quickest – way is to use Discover Mode. Simply open NetSpot and click the slider on the upper-left to change from "Survey" to "Discover." This will immediately take a snapshot of the surrounding area and report the signal strength of every wireless network within range. If you just need to measure your wireless network signal strength in one location, then Discover Mode is all you need.
However, if you wish to measure signal strength throughout your network area, you'll want to do a full site survey. Flip the switch back to "Survey" and start a new survey. You'll need to upload a map of your area that is drawn to scale, or you can draw one using NetSpot's map drawing tools. Read "How Do I Start My Survey?" if you haven't used NetSpot before.
Once you have completed your survey, there are three WiFi heatmap visualizations you will want to view. The first is Signal Level. This will show you the WLAN signal level throughout the area you surveyed. Blue and purple areas are places where the wireless network signal is weakest. Then you'll want to view the Signal-to-Noise Ratio heatmap. A lot of environmental noise (from microwaves, cordless phones, fluorescent lights, etc.) can make even a decently strong signal virtually unusable. Third, view your Signal-to-Interference Ratio – this measures the channel interference from other wireless networks. Again, the blue and purple areas are the ones of greatest concern.
Once you've identified areas of low Wi-Fi signal strength, you can take steps to correct it. Options include: moving an access point/router, adding a new access point, or installing a Wi-Fi signal repeater or a WiFi extender. If it's a high noise level that's the problem, you can take steps to reduce the noise by moving your access point, moving or shielding the interfering device, or switching from the 2.4 GHz band to the 5 GHz one. If the problem is high levels of interference, try changing channels to one with less interference. See these troubleshooting guides to learn more about signal level, noise level and channel interference.