There are a lot of different ways to look at this question and everyone seems to have their own version of how they make their decision in choosing the right ski length. We will keep things on the more simple side here and give you some general guidelines.
Start with your height in centimeters. If you don’t know your height in the good ol’ metric system then a quick Google search will convert it for you. From this number you can generally size up or down 15cm either way depending on skier level, style, etc.
A beginner should generally start at the lower end of the range, while a more advanced skier will likely prefer something longer.
If you already know what ski lengths you like from your resort skis and want to know how that translates to backcountry skis, here are a couple of tips. For skis with a traditional camber profile, and those designed for more technical terrain, you may want to choose a slightly shorter ski than you are used to skiing in a resort. This can help increase control and maneuverability in those tight couloirs or tree lines. For skis with a shorter effective edge, a rockered profile, and those designed for powder skiing, you can size up to get the right feel under your feet and the maximum float.
Some skiers may choose to do things differently. These guidelines are meant to be a good place to start. If you have additional questions feel free to reach out to us.