How to use the file transfer time calculator
- Enter the file size and choose its unit.
- Enter the link speed and choose its unit, in bits or bytes per second.
- Enter the overhead share, the part of the link lost to headers, retries and pauses.
- Read the transfer time and the table of the same file at other common speeds.
Formula
bits = file size x 8 x unit size (1,000 or 1,024 per step)
effective speed = link speed x (1 - overhead / 100)
time in seconds = bits / effective speed
Megabits per second use 1,000,000 bits; megabytes per second are 8 times that. A MiB is 1,048,576 bytes and a MB is 1,000,000 bytes.
One gigabyte over a 100 Mbps link
A 1 GB file is 8,000,000,000 bits. On a 100 Mbps link with 5 percent overhead, the effective speed is 95 Mbps, or 11.875 MB/s, so the file takes 84.21 seconds, which is 1 minute 24 seconds. At 10 Mbps the same file takes 14 minutes 2 seconds, and at 1 Gbps it takes 8.42 seconds.
A 50 GiB backup over a 300 Mbps link with 8 percent overhead moves at 276 Mbps and takes 25 minutes 56 seconds. A 4.7 GB disc image at 40 MB/s with no overhead takes 117.5 seconds, or 1 minute 58 seconds.
Bits, bytes and the two kinds of kilo
Internet speeds are sold in bits per second and file sizes are shown in bytes, and a byte is 8 bits, so a 100 Mbps link moves at most 12.5 megabytes a second. Storage makers use 1,000 for each step of KB, MB and GB, while operating systems often use 1,024 and call it the same name. The page offers both so you can match what you see.
Overhead is real but varies. A good wired link may lose a few percent to headers, and a shared wireless link can lose a lot more. If you have measured your real speed, enter it as the link speed and set overhead to 0.
Related tools
If a transfer is slower than expected on a distant link, check the window with the Bandwidth Delay Product Calculator. To estimate the size of an audio or video file first, use the Media File Size Calculator. For monthly totals, see the Monthly Data Usage Calculator, and for pictures, the Image File Size Calculator.
Assumptions and limits
- The speed stays constant for the whole transfer.
- Overhead is a single percent of the link and covers everything that is not file data.
- Sizes and speeds are entered as numbers up to 1,000,000,000 of their unit.
- The overhead shown when the page opens is an example, not a measured figure.
Frequently asked questions
Why is my download slower than the speed I pay for?
The speed is usually quoted in bits and is a best case. Protocol overhead, shared links, the server and your own device all lower what you actually get.
What is the difference between MB and MiB?
A MB is 1,000,000 bytes and a MiB is 1,048,576 bytes. For a GB against a GiB the difference is about 7 percent, which matters on large files.
Can I enter the speed in megabytes per second?
Yes. Choose megabytes per second in the speed unit list, and the page converts it to bits before dividing.
Why does a small file show a time in milliseconds?
When the time is under one second, the page shows milliseconds so it does not round to zero. A real transfer also has a start-up delay that is not included.