A good starting point is choosing a ski length that falls somewhere between your chin and the top of your head when you stand next to it. Shorter skis are easier to turn and maneuver, making them great for beginners, while longer skis offer more stability and better tracking at higher speeds.
Where you land in that chin-to-head range depends on how you ski. If you're a beginner or prefer making quick, short turns on groomed runs, size down toward your chin. If you're an advanced or aggressive skier who charges hard and prefers fast, wide turns, go longer toward the top of your head. Heavier riders for their height should also consider sizing up for extra stability.
Finally, don't forget to factor in the ski's profile. Rockered skis have tips and tails that curve upward, meaning less effective edge is actually touching the snow. Because of this, they "ski shorter" than traditional camber skis. If you're buying a rockered ski, you can confidently choose a longer length to get the stability you'd expect.