If your Internet connection isn’t living up to expectations, a bandwidth test is your first step to fixing the problem. This test calculates the maximum download and upload speed of a connection in megabytes per second  (Mbps) along with its ‘ping’, or the time it takes for your computer to transmit data and have a signal returned. This value is measured in milliseconds: The lower, the better.

Not all tests are created equal, however, and not all return the same results. Why? In part, it’s thanks to website servers—here’s how they can affect your bandwidth test.

ISP-Side Problems

The first ‘leg’ of your Internet connection relies on an ISP or Internet Service Provider. This is typically a telecommunications company that supplies cable or ADSL broadband services. Any data sent to your computer must be routed through the ISP’s server network—and could get bogged down if the network isn’t up to date or experiences a malfunction. Compare the value you’re getting from a bandwidth test against the speed promised by your ISP. If they don’t match, and if your latency is extremely high, the problem may be with your provider.

How servers impact a bandwidth test

Testing Servers

To measure your connection speed, bandwidth test sites use a network of servers. Typically, a single server is selected based on its geographical location—the closer to your home, the better the results. Some tests allow you to manually choose a server location and then run multiple tests to determine what your speed and ping look like under different conditions, while others assign a server with no option to change.

If the test you’re using consistently returns poor results, try several others and compare. Download numbers shouldn’t vary by more than 1 Mpbs—if they do, the servers of at least one speed test are either too far away or are processing too many requests at once.

How do servers affect your bandwidth test? If they’re bogged down or too far away, you may see lower numbers than expected.