Calculating Download Times

Let’s say you have this file that you allow your visitors to download, and you want to show them a helpful estimation of download time. How do you do this?

1. Find out which connection they’re using — 56.6 kbps, T1 (1.544 mbps), Cable, DSL, etc. Cable/DSL are also available at fractional speeds like 256kbps, 386kbps, 512kbps, or 768kbps so you need to decide which ones you want to present your user.
2. We need to convert both the file size and the connection speed to a common measuring unit, which can be bytes or bits. I’ll use bits for this example (connection speeds are already in bits. So 56.6kbps = (56.6 * 1024) = 57,958.4 bits).
3. Do the same thing with the file size — say your file is 50KB… Multiply it by 1024 to get the file size in bytes. So 50 KB * 1024 = 51,200 bytes. Multiply that by 8 to get it in bits: 51,200*8 = 4,09,600 bits

1. Now divide the file size by the connection speed — 4,09,600/57,958.4 = 7.06 seconds

Download Time Calculator is a script that will give you download times for various connection types based on the file size you provide.