Right, but all standard monsters of a given level are worth the same number of XP. A level 1 (non-minion) kobold is worth 100 XP; so is a level 1 goblin, or a level 1 beetle, or....etc. So if you're crafting a level 3 encounter for a party of 4 characters, the guideline is to use (4 * 150)=600...