Internet & Digital Calculators
These two calculators translate between file sizes and connection speeds, which are quoted in different units and routinely confused. Anyone downloading a large file, planning a video stream or choosing a broadband package benefits from checking the figures before committing. The Download Time Calculator takes the size of a file and the speed of your line and estimates how long the transfer will take. It is the quick answer to whether a game update will finish before you go out, or whether a client can reasonably be sent a video rather than a link. Remember that speeds are advertised in megabits while files are measured in megabytes, an eightfold difference that the calculator handles for you. The Bandwidth Calculator works at the level of a connection rather than a single file. Give it the number of users or streams and the quality each needs, and it estimates the capacity required, which is what you want when sizing office internet, planning a live broadcast or working out whether a household can watch two 4K streams while someone else is on a video call. Use the download tool for one-off transfers and the bandwidth tool for sustained, simultaneous use. Both run in your browser with no sign-up and nothing recorded.
2 tools available
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Bandwidth Calculator
Convert between file size, connection speed and transfer time, with an adjustable overhead allowance.
Download Time Calculator
Estimate download duration from file size and connection speed, with a comparison across common speeds.
Normalising everything to bits before dividing
With both sides in bits, time in seconds is total bits divided by bits per second. That figure is broken into days, hours, minutes and seconds, and converted back into a bytes-per-second throughput you can compare with your download manager.
The eightfold relationship between bits and bytes is the source of most confusion about broadband speed. Internet providers advertise in megabits per second while operating systems and download managers report in megabytes per second, so a connection sold as 100 Mbps delivers around 12.5 MB/s at best. Real-world throughput is typically lower than the advertised figure because of network congestion, protocol overhead and the capacity of the server you are downloading from.
A 4 GB film on a 50 Mbps connection
Dividing 32 billion by 50 million gives 640 seconds, which the tool displays as 10 minutes and 40 seconds. The throughput figure is 50 million bits per second divided by 8, which is 6.25 million bytes per second, or 6.25 MB/s.
The comparison table makes the effect of speed tiers concrete. On 25 Mbps the same file takes 1280 seconds, which is 21 minutes and 20 seconds, exactly double. On 100 Mbps it takes 320 seconds, or 5 minutes and 20 seconds. On a 1 Gbps connection, 32 billion bits divided by 1 billion bits per second gives 32 seconds.
Scale up to the 60 GB 4K film preset on that same 50 Mbps line and the arithmetic becomes 480 billion bits divided by 50 million, which is 9600 seconds, or 2 hours and 40 minutes.
Why the real download is usually slower
Several factors account for the difference. Protocol overhead means some of the bits on the wire are headers rather than file content. The server at the other end may cap per-connection speed or be busy. Wi-Fi adds its own losses, and a device several rooms from the router can run at a fraction of the wired rate. Other devices streaming or backing up at the same time share the same pipe. Evening peak hours are measurably slower than early morning on many networks.
Use the calculator for planning rather than prediction: it answers whether a transfer is a coffee break or an overnight job, and the comparison table answers whether a faster tier would actually change your day.