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Free Download Speed Test

Measure your real download speed by fetching test data directly from our global CDN. The test uses a timed measurement window, reports Mbps and MB/s, and compares your result to 4G, 5G, and fiber benchmarks.

Source: cdn.truefilesize.com

How the speed test works

1. You select a CDN chunk size from 1MB to 100MB. The test may repeat that chunk until the timed measurement window is complete.

2. The browser downloads directly from cdn.truefilesize.com using XMLHttpRequest with progress tracking. CDN CORS headers allow the browser to read download progress without routing the measurement through localhost or an app proxy.

3. We ignore the first 500ms as warm-up, then measure throughput over an 8 second window.

4. Final speed is the weighted average of bytes downloaded during that measured window, converted to Mbps. Max throughput mode uses parallel CDN downloads for a closer Speedtest-style estimate.

A cache-busting query parameter ensures each test downloads fresh data with no browser cache interference.

Internet speed benchmarks

ConnectionTypical speedDownload 100MB in
3G Mobile5 Mbps~160 sec
4G LTE20 Mbps~40 sec
5G100 Mbps~8 sec
Cable/DSL50-200 Mbps4-16 sec
Fiber500-1000 Mbps<2 sec

Frequently Asked Questions

How accurate is this speed test?
It is a practical estimate of real browser download throughput from our CDN. We use direct CDN downloads, cache-busting, a short warm-up period, and an averaged measurement window. Results can still vary due to network congestion, CDN edge proximity, TCP slow-start, Wi-Fi quality, VPN overhead, and the number of streams selected. Use Max throughput mode for a closer Speedtest-style peak estimate.
Why is my speed lower than my ISP advertises?
ISP speeds are 'up to' maximums, rarely achieved consistently. Factors include Wi-Fi vs ethernet, network congestion during peak hours, distance to the CDN edge, VPN overhead, and shared bandwidth. Test on ethernet for the most accurate baseline.
What is the difference between Mbps and MB/s?
Mbps = megabits per second, which is how ISPs advertise speed. MB/s = megabytes per second, which is how files download. 1 MB/s = 8 Mbps, so a 100 Mbps connection downloads at about 12.5 MB/s.
Does this test measure upload speed?
No. This tests download speed only, which is what matters for browsing, streaming, and file downloads. For upload speed testing, use a service that sends data from your browser to its servers.
Can I test download speed programmatically?
Yes. Download our test files directly: curl -o /dev/null -w '%{speed_download}' https://cdn.truefilesize.com/test/test-100mb.bin. Or visit our Download Tests page for files from 1MB to 10GB.

Need larger files for manual testing?

Visit our Download Tests page for files from 1MB to 10GB - perfect for manual speed testing, upload API stress tests, and bandwidth benchmarking.

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