You are best to ask your local dealer. They can help you find your most suitable length and can discuss this in detail with you. It can be difficult to find the right size as it depends on your skill level as better skiers normally prefer longer skis than intermediate/beginner skiers. It also depends on the model, as freeride skis should be longer than for example On-Piste slalom skis. As a general rule the correct ski length is somewhere between chin and top of the head.