Hey guys thinking of making my own encounter. Pretty new to DM'ing.
If I have 4 1/4 CR skeletons fighting a 4 man party of level 1's. Is it equivalent to a CR 1 Ghoul fighting the party?
And does this scale well e.g. 2 CR 2 creatures = 1 CR 4.
You should read the relevant chapter in the DMG. It starts on page 811.
CR is not supposed to be treated that way (ie multiplied, summed etc). The XP value of the monsters is closer to what you want, but still not exactly. Multiple monsters pose a bigger threat than fewer ones. To balance this the DMG uses XP multipliers based on the number of enemies.
Also note that an encounter can be dramatically different based on other factors, such as terrain or ambushing. Balancing is more of an art than a hard science.