Top 3 Causes of Slow WiFi

     One of the most common questions in the world of WiFi is, “Why is my WiFi slow?” This article is intended for anyone who runs a WiFi network, and especially non-IT-experts, to really help troubleshoot this question to its fullest extent and identify top causes.  The article increases in complexity with each step. 

Tools Needed 

     While there are many tools in the WiFi industry ranging anywhere from free to thousands of dollars, here are a few basic tools that are easy to obtain: 


  • inSSIDer - can be downloaded for free here
  • WiFi adapter - from this list.
  • Wi-Spy DBx spectrum analyzer (optional) - can be purchased here


Cause 1: Insufficient WiFi Coverage

     Do you have sufficient WiFi coverage? One of the leading causes of slow WiFi is insufficient coverage. The free version of inSSIDer can help you with this.  

     Open inSSIDer and walk around to each area in your home or office environment that requires reliable WiFi. Find your wireless network’s name, or SSID, and take note of its signal strength in the Signal column. A reliable signal strength to strive for is at least -67 dBm or higher (-60, -50, -40 dbm, etc). For media hungry households with streaming video, you might even want to strive for -60 dBm or higher. Anything lower than this (-70, -80, -90 dBm) means that the AP or router is too far away. The farther away you are from your router or AP, the lower the data rate, meaning slower WiFi. You can read more about signal strength and data rates here

                    -55 dBm indicates good coverage

                    -74 dBm is not ideal coverage

     If you find that you have poor coverage (-70, -80, -90 dBm, etc.), you will either need to move the AP and client closer to each other, or add another AP. 

Cause 2: Not “Steering” Clear of the 2.4 GHz Band

     What frequency band are you using? All too often, the culprit of slow WiFi is use of the 2.4 GHz band, which offers slower data rates and is often oversaturated with WiFi and non-WiFi devices, like microwave or baby monitors. 

The FCC allows WiFi to operate in two different frequency bands, the 2.4 and 5 GHz. 


     How do you know if the 2.4 GHz band is oversaturated? Well, you can’t… unless you have a spectrum analyzer.  Since RF is invisible to the naked eye, you must use a spectrum analyzer like the Wi-Spy DBx in order to see it. With a Wi-Spy DBx plugged in, inSSIDer will show you exactly how much the spectrum is being utilized and display any significant interferers. The image below shows a cordless phone wreaking havoc on channels 3-7, which would otherwise be invisible without a Wi-Spy.  

                    This interferer will slow WiFi down on channels 3-7

     OK, how do you know if any clients are using the 2.4 GHz band?  Luckily, with a MetaGeek Plus subscription and compatible wireless adapter, inSSIDer can show you by diving into the Radio Details. To find out exactly which clients they are, click the binoculars

binoculars.png icon.

     Most WiFi devices are designed to steer back and forth from one band to another as they move around.  Since the 2.4 GHz wavelength is longer and pierces through walls and material more easily, devices will use the 2.4 GHz band as they get farther away from the router or AP. However, sometimes they get stuck on the 2.4 GHz band even when they are close enough to use the 5 GHz.

      In the example above, a ChromeCast and Apple device are associated to the 2.4 GHz band. The 1st generation ChromeCast is not capable of using the 5 GHz band and therefore won’t be steering to it anytime soon. The Apple device, however, can and should steer to the 5 GHz band whenever possible. It would be a good idea to turn the WiFi on that device off and on again to ensure it’s choosing the optimal band. 

     Unless you have some old device like a Nintendo Wii or 1st generation ChromeCast, you might consider turning off the 2.4 GHz radio entirely, forcing all traffic to the 5 GHz band. If you need the 2.4 GHz band, you can simply give each band its own SSID to segment clients and to ensure they don’t steer down to the 2.4 GHz band. Once your devices are using the frequency band that you want, be sure to choose non-overlapping channelschannels 1, 6, or 11! 

Cause 3: Insufficient Client and Router Capabilities

     Not all WiFi devices are created equal!  Another big reason for slow WiFi is that the WiFi devices simply aren’t capable of faster speeds. If you have sufficient coverage throughout the environment and your WiFi still seems slow, it might be a good idea to investigate the client and router capabilities. And you guessed it, inSSIDer can help with this too. 

     To check the MCS index and number of spatial streams that your client or router can use, simply click on the binoculars icon.


     In the above example, the iPhone 7 has 2 spatial streams and a max MCS Index of 9. The MCS Index tells us that the max data rate this iPhone can achieve on this network is 867 Mbps. Even if the ISP guarantees 10 Gbps ultra-high-fast download speeds, this iPhone will only reach 867 Mbps on this network. Inversely, some WiFi devices are bottlenecked by ISP backend speeds (see: Idaho). While a file transfer on the local network may benefit from high WiFi data rates, a MacBook Pro with 3 spatial streams using MCS 9 will only reach 100 Mbps per if the ISP data plan is only providing 100 Mbps. 

     There you have it--inSSIDer can thoroughly check for WiFi coverage, display client distribution per radio, and even show you which clients are hogging the bandwidth, all helping to solve the ever-expanding question of, “Why is my WiFi slow?

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From above mentioned discussion of slow wifi i have lernt a lot to overcome this issue