Well there's more to consider than just your height. If you're 6'2" but weigh 135lbs you shouldn't be riding a 170cm.

Generally you want it to hit between the bottom of your chin and your lower lip. if you're a beginner it should be a bit shorter. Just about at your chin. But like I said, weight also effects it. If you're really thin you might want to try something just below your chin. The smaller the board, the eaiser it is to ride, but the less surface area you have to keep you sliding.

Before anyone argues about sizing with me, I worked at a ski resort sizing people for rental equipment for a long time. I'm trained, you're not. Shutup.