According to Blizzard, the minimum requirements for PC include an Intel Core 2 Duo or an AMD Phenom II X3 720 with 2GB of RAM, 45GB of HDD space, and an NVIDIA GeForce GT 440, AMD Radeon HD 5680, or Intel HD Graphics 5000 or better. The recommended hardware will require players to at least own an Intel Core i5-3330 processor or an AMD FX-6300 or better, with 4GB of RAM, and NVIDIA GeForce GTX 750 Ti or an AMD Radeon R7 260X GPU or better.
As for gamers who plan on playing the game on their Mac, they will need to run at least OS X 10.10 or later, and have a Mac that is powered by an Intel Core i5-750 or better. GPU options include a minimum of an NVIDIA GeForce GT 640M or an ATI Radeon HD 4850, or an Intel HD Graphics 5000. Recommended GPUs include the NVIDIA GeForce GT 775M or an AMD Radeon R9 M290X.
Mac gamers will need to have more RAM than their PC counterparts with a minimum of 4GB of RAM, and a recommended 8GB. Installation space remains the same at 45GB. However Blizzard notes that it is possible that the system requirements could change in the future, but this is what we are looking at for now, but basically if you can run Warlords of Draenor, then you should be able to run Legion without much issue.