Although gigabytes and hours are not synonymous, functionally you can convert them to determine how long it might take to download or upload a very large file. The resulting value is largely determined by your Internet connection speed, but sometimes the limiting factor will be the speed of the website, if you're connecting to slow servers. In most cases, you'll make your calculation based on your connection speed.
Determine your Internet connection speed. You can do this by calling your Internet service provider, or you can test the speed yourself using one of the online speed tests (see References).
Convert your Internet speed into gigabytes per hour. Most connections will be given to you in Mbps, or megabits per second. To convert the speed measurement into gigabytes per hour, you multiply it by 0.4191. As an example, if your speed was 3.0 megabits per second, then your speed in gigabytes per hour would be 1.2573.
Find out how big the file is. If you were trying to download a legal, copyright-free DVD, then the size might be around 4.0 gigabytes.
Divide the file size by your download speed. In the example, the 4.0 gigabyte file divided by a speed of 1.2573 gigabytes per hour, would result in a download time of 3.18 hours.