Unless you later decide you need to raise the bars a lot, you can leave some height adjustability when you cut the steerer initially. Cut the steerer too long and add spacers above the stem, say 20 mm or so. Ride in that configuration for a while to determine where you prefer the bar height. During the trial period you can shuffle spacers between the top and under the stem to change the height. When you have settled on a preferred height, cut the steerer to its final length but leave enough extra for a 5 or 10 mm spacer above the stem for future adjustment.
Note that most carbon steerer fork makers limit the spacer stack under the stem to 40 to 50 mm maximum so don't try to set the bars too high if you have one of these forks.