What are APM and EPM in Starcraft 2?

[Valks 2,373]

While they are not necessarily terms that are specific to Starcraft, APM and EPM are widely used when discussing the playstyles of different players, as well as when looking at ways to improve. As a lower ranked player, you might be told to try and increase your APM or EPM, depending on how you play. So what exactly are they?

APM stands for Actions Per Minute, a standard measurement that essentially shows how much you are doing per minute in the games you play. As you would expect, the higher your APM, the better of a player you can be (keep in mind that this is not a definite metric and high APM does not automatically guarantee high skill).

APM can be anything from selecting units and giving out orders to building structures and so on. The more things that you can do in a certain timeframe the better, since it means your opponent is going to be more occupied with trying to respond to you. If you can heavily outpace their APM, you can ensure that fights swing in your favour by flustering them with multiple attacks on different points.

APM, however, encounters a problem when quantifying "skill" - it doesn't distinguish what your action is in any way. It simply acknowledges that an action happened, regardless of whether you actually did anything of use. 

To counter this issue, something called EPM was created - this stands for Effective Actions Per Minute, which only acknowledges when your action achieves something by giving a command, as opposed to a random action that can have no impact but still be counted in APM.