@New to i30. I'm going to assume that you don't have your owners manual or you couldn't easily find the info in it.
My manual (i30 2018 SR petrol) states that the drain and refill volume is 4.5L (hidden in Specifications and Consumer Information, Chpt 8.

). I'd assume that your engine would be the same or close to it
I'd buy 5L, pour in say, 4.25L, run engine to operating temperature, stop, take a dipstick measurement on flat ground after say, 2 minutes and add oil as required.
Hope that helps.