Start with the basics.

 

Connect a PC via ethernet cable direct to the modem (bypass router) to ensure you have a good and fast connection your ISP using one of the speed tests. 

 

Next with the PC connected to the router via ethernet cable, compare the results with the PC vaules from the PC connected to the modem. 

 

Be sure to use good cables, as that is a source of many issues.  Use high quality connectors on the cable lines up to the modem and as few as possible. A ‘home run’ from the cable box to the modem is best.

 

I use a good UPS that has voltage control for my Modem and router.

 

Be sure you have a good ethernet cable between the modem and router.

 

Placement of the router as to location, height, direction it faces, direction of antennas if any affects distance and coverage as does anything in between. Many times small changes in location, direction, and height makes a difference as signals get blocked and bounced around.  

 

WIFI has two Bands - 2.4 GHz and 5 GHz.

The 2.4 GHz is slower but works at father distances.

The 5 GHz is faster but not does work as well at distance.

The SSIDs should be different for best performance and enables you to put specific devices on a specific band. For example, you may want to put printers on the slower band and your PC on the faster band. Also do not use the default SSID userids and passwords as others may jump on your WIFI. 

WIFI devices have different standards such as 802.11A, 802.11B, 802.11G, 802.11N, and 802.11AC. “11A” and “11C” are the oldest and very rare if any devices uses it today. “11G” is an older and slowest of devices in use today. Next was “11N’ which is faster. The current standard is “AC”. Routers will support the older versions such as a “N” router will support both “G” and “N” standards and an “AC” router will support all previous standards. 

Also on some routers, WIFI will slow down to the slowest connected device so if you have an old “G” device, it may be slowing your WIFI down to “G” speeds. Power off all of your WIFI devices and test with only your test device connected.

 

Then of course the device you are testing the WIFI speed may be an issue as the WIFI driver in the device may be the limiting factor.

 

Other devices may be interfering with the radio signal. Things like cordless phones, wireless security cameras, anything wireless that uses the 2.4 or 5 bands.

 

Other WIFIs may be flooding the channel your WIFI is using. Each location will have its own best channel and that can vary from time to time. I have a iMac and it has tools (although somewhat hidden) that allow me to see the other nearby SSIDs and the bands/channels they are using. There are WIFI scanners that you can install for Windows machines. I have my router channels set to Auto which works okay for me.  Selecting a specific channel may be needed if something is interfering with channel the router selected to use.

 

If you use a VPN, it will result in a slower speed. 

 

Hope this helps.