Fit it, then put chain on small (granny) ring on cranks. Then, put chain on lowest(smallest) cog on the cassette.
From here look at the rear mech, in the general area of the jockey wheels. Does the chain at the lowest point touch the top jockey wheel? If there is a gap, doesn't matter how big or small , just any gap, then chain is fine as it is.
But, generally it's too long so use your hands to gather up a few links until the rear mech cage pulls forward and, therefore creates a gap between chain and top jockey wheel. From here you be able to determine how many links to take out, if necessary.
cheers.