What the Four Numbers Mean
Download speed (Mbps) is how fast your connection pulls data from a server — the number most people mean when they talk about "internet speed." It governs how quickly web pages load, how smooth video streams, and how fast files arrive.
Upload speed (Mbps) is how fast your device sends data to a server. Most residential plans are asymmetric — upload speeds run significantly lower than download. Upload speed matters for video calls, live streaming, cloud backups, and sending large files.
Ping (ms) is round-trip latency: the time between sending a request and receiving the first response. Lower is better. Below 20 ms is excellent for gaming and VoIP; above 100 ms starts to feel sluggish in real-time applications.
Jitter (ms) is the variation in ping across multiple samples — the standard deviation of round-trip times. A connection with 30 ms average ping and 2 ms jitter is stable. The same 30 ms ping with 40 ms jitter produces noticeable audio glitches on calls and lag spikes in games.
How the Test Works
The download test fetches a large file from Cloudflare's speed test infrastructure and measures throughput by tracking bytes received over time using the Fetch API with a streaming reader. Multiple samples are averaged to reduce single-measurement noise.
The upload test POSTs random data to the same endpoint and measures throughput from timing. Ping is measured by timing a series of small round-trip requests before the main tests run. Jitter is the standard deviation of those ping samples.
Mbps vs. MBps — a Common Confusion
Speed test results are in megabits per second (Mbps). File sizes are measured in megabytes (MB). There are 8 bits in a byte, so to find your effective download speed in megabytes per second, divide by 8.
Example: a 100 Mbps connection downloads at roughly 12.5 MB/s — a 1 GB file takes about 80 seconds, not 10. ISPs advertise in Mbps for the same reason: the numbers look larger.
What Affects the Result
A speed test measures the connection between your device and one server at one moment. Results vary with:
- Time of day — shared infrastructure (cable, DOCSIS) slows during peak evening hours when many users are online simultaneously.
- WiFi vs. ethernet — a wireless connection adds its own bottleneck independent of your ISP plan. A slow WiFi result may reflect the router, not the internet line.
- Background activity — software updates, cloud sync, or other devices on the same network consume bandwidth during the test.
- VPN — routing traffic through a VPN adds latency and typically reduces throughput.
- Test server location — this tool tests against Cloudflare's nearest edge node. A geographically closer server shows lower ping regardless of your ISP's broader performance.