There are a bunch of websites online you can use to check your Internet speed. Just click the button!
Generally, it's best to do an Internet speed test at the modem since WiFi and the computer's router may not be fast enough to deliver maximum speeds. If you want the most accurate result, connect your device directly to the Internet source (modem, gateway, or Fiber ONT) with a network cable. This means the modem and router can't negatively impact the test if they're slow.
Learn how to check how fast is your internet connection.
