File Transfer Time Calculator
Work out roughly how long a download, upload or backup will take over a given connection, with an allowance for real-world overhead.
🔒 Runs entirely in your browser. Nothing you type is sent anywhere.
How to use it
- Enter the file or backup size and its unit.
- Enter your connection speed. Internet plans are quoted in megabits (Mbps); disk and LAN speeds are often in megabytes (MB/s).
- Pick a real-world efficiency. Transfers rarely hit the theoretical maximum because of protocol overhead and congestion.
Bits versus bytes, the usual trap
A 100 Mbps connection is 100 megabits per second, not megabytes. There are 8 bits in a byte, so 100 Mbps is about 12.5 MB/s at best. This is why a “100 meg” line downloads a 1 GB file in roughly a minute and a half, not ten seconds. The calculator handles the conversion for you.
FAQ
Why is my real transfer slower than the theoretical figure? TCP overhead, disk speed at either end, Wi-Fi, and a busy link all take a cut. The 90% default is a reasonable everyday allowance; drop to 70% for a congested or lossy connection.
Is anything sent to a server? No. The maths runs in your browser.