Internet Speed Test

An internet speed test measures the throughput of your current connection by timing how long it takes to transfer a known amount of data and reporting the result in megabits per second. A speed test also measures latency, the round-trip time between your browser and a reference server, expressed in milliseconds.

This browser-based Speed Test performs a small fetch against Cloudflare’s cdn-cgi/trace endpoint to measure latency, then times the read of a 1 MB in-memory blob to estimate local throughput. The numbers it returns are a quick health check rather than a definitive bandwidth measurement: real ISP-grade tests like Speedtest.net or fast.com transfer hundreds of megabytes against geographically distributed servers and parallel TCP streams. Use this tool when you need a fast sanity check, when you want to see whether latency just spiked, or when you are comparing two browsers or networks side by side.

Why use Speed Test?

• Get a latency check without installing anything. The tool measures round-trip time to a Cloudflare edge in one click, which is enough to confirm a connection is alive and responsive.
• Compare two browsers or profiles fast. Run it in normal and incognito modes back to back to see whether an extension is slowing your traffic.
• Spot obvious throughput drops. A connection that was reporting 100 Mbps yesterday and 8 Mbps today on the same test has a real problem worth investigating with a heavier tool.
• Estimate worst-case load times. Combine the reported throughput with your page size to forecast how long a fresh visitor on the same network would wait.
• Stay private. Unlike many speed-test sites, this one does not require a server-side endpoint, an account, or third-party analytics to run.

How to use the Speed Test

1. Close other tabs and apps that might be downloading in the background, including video calls and cloud sync.
2. Click Run Speed Test.
3. Wait while the tool issues a latency ping and then times a 1 MB blob read.
4. Read the four result cards: Latency, Download Speed, Download Time, and Test Size.
5. Re-run on a different network or browser to compare.

How browser speed tests work

A browser speed test cannot open raw sockets, so it works by issuing HTTPS requests and measuring the time performance.now() returns before and after. Latency is the time to complete a small HEAD request. Throughput is the size of a downloaded payload divided by the time the browser took to receive it, multiplied by 8 to convert bytes to bits.

const start = performance.now();
const response = await fetch(url);
await response.blob();
const seconds = (performance.now() - start) / 1000;
const mbps = (bytes / seconds / (1024 * 1024)) * 8;

The accuracy of the result depends on the payload size, the server location, the number of parallel streams, and whether the network path is saturated. Heavy tests use payloads in the hundreds of megabytes, multiple TCP streams, and globally distributed servers to reach line rate. A 1 MB single-stream test in one browser tab will under-report a gigabit connection by an order of magnitude but is still useful for spotting outages and latency spikes.

What affects measured speed

Many factors between your browser and the test server influence the number you see. The table below covers the most common ones.

All measurement runs in your browser using the fetch and performance APIs. The latency request touches cdn-cgi/trace on Cloudflare’s edge to time the round trip; the throughput portion reads a blob generated locally, so it does not consume bandwidth on a remote server. Nothing is uploaded to a third party.

Mbps vs MB/s

Speed tests report megabits per second (Mbps). File sizes use megabytes per second (MB/s). One byte is 8 bits, so:

100 Mbps = 100 / 8 = 12.5 MB/s
1 Gbps   = 1000 / 8 = 125 MB/s

When a file manager says a download is moving at “10 MB/s” on an “80 Mbps connection,” the two numbers agree (10 × 8 = 80). Confusing Mb with MB is the single most common mistake people make when interpreting speed-test results.

Common use cases

• Remote workers diagnosing call quality issues. Run the test before joining a video meeting to verify latency is under 50 ms and throughput is adequate.
• Developers benchmarking dev-server performance. Compare the local blob test across browsers to see if one engine is unusually slow on cold reads.
• IT support staff triaging a “the internet is slow” ticket. Walk a user through a quick check before escalating to the ISP.
• Travelers comparing hotel Wi-Fi networks. Pick the access point with the lowest latency on a one-click test before committing to a long call.
• QA engineers reproducing slow-network bugs. Establish a baseline with the tool, then throttle in DevTools to simulate a regression.

Frequently asked questions

How accurate is this speed test?

The tool returns a useful sanity check, not a calibrated bandwidth number. The 1 MB single-stream payload under-reports any connection faster than about 100 Mbps. For accurate measurements, use Speedtest.net, fast.com, or your ISP’s official tool, which open multiple parallel streams against regional servers.

Why is my speed lower than my ISP plan?

Plans advertise the peak rate of your line to the ISP’s edge. Real measurements deduct overhead from Wi-Fi, the modem, the path to the test server, and any background traffic. A plan rated 200 Mbps often shows 140–180 Mbps on Wi-Fi and 190+ Mbps on a wired test, both of which are normal.

What is a good ping or latency?

Under 30 ms is excellent and supports gaming and video calls without noticeable delay. 30–80 ms is fine for most use. Above 150 ms makes video calls feel laggy. The latency this tool reports is the round trip to a Cloudflare edge, which is usually under 50 ms on a healthy connection in a major city.

What is the difference between download and upload speed?

Download speed measures how fast data flows from the internet to your device. Upload speed measures the reverse. Most home connections are asymmetric, with download many times faster than upload, because residential traffic is mostly downstream. This tool measures latency and a download-side throughput estimate.

Does this speed test send any data about me?

The tool issues one HEAD request to Cloudflare’s cdn-cgi/trace endpoint for latency. The throughput portion reads a blob generated locally in your browser, so no bandwidth is used at the server side. No analytics, no account, no log of your IP beyond the standard Cloudflare access log.

Why does my speed change every time I run the test?

Network throughput is noisy. Wi-Fi contention, CPU load, browser background tasks, and ISP-side queueing all affect the time the browser measures. Running the test three times and taking the median is more reliable than a single shot.

Does the test work over a VPN?

Yes, but the VPN adds latency and reduces throughput because every packet is encrypted and tunneled through the VPN exit. Comparing results with the VPN on and off is a fast way to see how much overhead the tunnel introduces.

Why does the test fail on some corporate networks?

Some corporate firewalls block requests to Cloudflare’s cdn-cgi/trace endpoint or restrict the no-cors mode the test uses. If the latency request errors out, try a different network or check your corporate proxy policy.

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