Download Time Calculator
Estimate how long a file takes to download from its size and your connection speed.
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How to use this tool
Estimate a file transfer before starting it. File size is normally quoted in bytes, while broadband speeds are normally quoted in bits per second, so the units matter.
- Enter the file size and choose its unit, keeping GB and GiB distinct.
- Enter the available connection speed and its unit.
- Choose the usable percentage of that speed to allow for other traffic and overhead. Compare the estimate with the full-speed result.
Worked example: a 5 GB download
One byte contains eight bits. A decimal 5 GB file contains 40,000 megabits. At 100 Mbps, the ideal duration is 40,000 ÷ 100 = 400 seconds, or 6 minutes 40 seconds. At 80% usable speed, divide by 80 Mbps instead: 500 seconds, or 8 minutes 20 seconds.
Why a real transfer takes longer
Your Wi-Fi, other devices, the file server and protocol overhead can reduce usable throughput. GB uses powers of 1,000; GiB uses powers of 1,024, so the same displayed number represents a different file size. The estimate assumes a steady speed throughout. Use a recent measured download speed rather than a package’s advertised maximum when possible.
Your progress and privacy
No account is needed. Personal bests, preferences and saved progress stay in this browser where supported. They do not sync between devices. Keyboard and mouse test events are never saved. You can clear saved activity from the home page; the privacy notice explains consent and measurement.
Common questions
- Does the calculator download my file?
- No. It uses the size and speed you enter. It does not select, upload or download a personal file.
- Why is 100 Mbps not 100 MB per second?
- The lowercase b means bits and uppercase B means bytes. At eight bits per byte, 100 Mbps is 12.5 MB per second before overhead.