Internet Speed Test: How It Works and What the Numbers Mean

What Happens When You Run a Speed Test

When you hit the start button on a speed test, your browser performs a series of network measurements against a test server. It downloads a chunk of data, uploads a chunk of data, and measures how long each operation takes. It also sends tiny packets back and forth to measure latency. The results tell you how fast your internet connection is performing right now, but understanding what those numbers actually mean requires a bit more context.

Download Speed

Download speed measures how quickly data travels from the server to your device, expressed in megabits per second (Mbps). This is the number most people care about because it affects streaming, browsing, and downloading files. A 100 Mbps connection can theoretically download a 1 GB file in about 80 seconds. For reference, Netflix recommends 5 Mbps for HD streaming and 25 Mbps for 4K.

Upload Speed

Upload speed measures how fast data travels from your device to the server. Most home connections have significantly slower upload speeds than download speeds (this is called an asymmetric connection). Upload speed matters for video calls, live streaming, uploading files to cloud storage, and online gaming. If your video calls are choppy but streaming works fine, poor upload speed is likely the culprit.

Latency (Ping)

Latency, often called ping, measures the round-trip time for a tiny packet of data to travel from your device to the server and back, measured in milliseconds (ms). Low latency means responsive connections. Under 20 ms is excellent. Under 50 ms is good for most uses. Over 100 ms and you will notice lag in video calls and online games. Latency is independent of bandwidth. You can have a fast connection (high Mbps) with high latency, which feels sluggish despite the raw speed.

Jitter

Jitter measures the variation in latency over time. If your ping is consistently 30 ms, jitter is low and your connection is stable. If your ping jumps between 15 ms and 200 ms, jitter is high and real-time applications (calls, gaming, streaming) will stutter and buffer. Low jitter is as important as low latency for a smooth experience.

What Affects Your Speed Test Results

WiFi vs Ethernet: WiFi adds latency and reduces throughput. Walls, distance from the router, interference from other devices, and the WiFi standard (WiFi 5 vs WiFi 6) all affect performance. For the most accurate test, connect via ethernet cable directly to your router.

Time of day: Internet speeds often drop during peak hours (evenings and weekends) when your neighbors are all streaming. ISPs may also throttle certain types of traffic during congestion.

VPN overhead: Running a VPN encrypts your traffic, which adds processing overhead and routes data through an extra server. Expect 10 to 30 percent speed reduction with a VPN active. This is normal. If you see a much larger drop, try a different VPN server or protocol. Check our WiFi security checklist for optimizing your network setup.

Server distance: The physical distance between you and the test server affects results. A server across the country will show higher latency and often lower speeds than one nearby. Most speed tests automatically select the closest server.

How to Get Accurate Results

Close all other tabs and applications. Disconnect other devices from your network if possible. Use a wired connection. Run the test multiple times at different times of day. Compare results across different speed test tools. A single test is a snapshot, not the full picture.

Your Speed vs What You Are Paying For

ISPs advertise speeds "up to" a certain number. You will rarely hit that maximum consistently. If your speeds are consistently below 70 percent of what you are paying for, contact your ISP. Document your test results over several days at different times. Run a speed test now and check your connection details to see your full network profile.