Free Data Transfer Calculator Online

About This Tool

This calculator works out how long a file or a data volume takes to transfer at a given connection speed, and the reverse. The key detail it handles for you is the difference between bits and bytes: connection speeds are quoted in megabits per second while file sizes are in megabytes, and there are eight bits in a byte, so a 100 Mbps link moves roughly 12.5 megabytes per second, not 100.

It also distinguishes decimal units (a megabyte as 1,000,000 bytes) from binary units (a mebibyte as 1,048,576 bytes), which is why a download can appear slower than the advertised speed suggests. Overheads such as protocol headers and shared bandwidth mean real transfers are usually a little slower than the theoretical figure, so treat the result as a best case.

Real-world transfers rarely hit the theoretical figure, because protocol overhead, shared bandwidth, disk speed, and network congestion all take a share. Treat the result as a best case and expect the actual time to run somewhat longer, especially over the internet where the slowest link on the path sets the true ceiling.

How to Use It

1. Enter the file size and its unit.
2. Enter your connection speed in the correct unit (megabits or megabytes per second).
3. Read the estimated transfer time, remembering it assumes the full advertised bandwidth.