--limit-rate

Specify the maximum transfer rate you want curl to use - for both downloads and uploads. This feature is useful if you have a limited pipe and you would like your transfer not to use your entire bandwidth. To make it slower than it otherwise would be.

The given speed is measured in bytes/second, unless a suffix is appended. Appending 'k' or 'K' counts the number as kilobytes, 'm' or 'M' makes it megabytes etc. The supported suffixes (k, M, G, T, P) are 1024-based. For example 1k is 1024. Examples: 200K, 3m and 1G.

The rate limiting logic works on averaging the transfer speed to no more than the set threshold over a period of multiple seconds.

If you also use the --speed-limit option, that option takes precedence and might cripple the rate-limiting slightly, to help keep the speed-limit logic working.

Starting in curl 8.19.0, the rate can be specified using a fraction as in 2.5M for two and a half megabytes per second. It only works with a period (.) delimiter, independent of what your locale might prefer.