You can find combo water skis in sizes ranging from 59 inches to 68 inches (159 to 172 centimeters) in length. Theoretically, you should pick the size of ski that matches both your bodyweight and athletic ability. But if you're buying a pair of combos that you may be sharing with other people, buy long. Anybody 110 pounds (49.8 kilograms) or more can handle a 67-inch ski, and the longer a ski is, the slower and more stable it tends to be, which is what you want if you're learning [source: Waterskis.com].
Ski length is a much more crucial issue once you've advanced enough to start using a single slalom ski. For slalom skiing, the right size ski largely is a factor of your physical proportions, and to a lesser extent, how adept a skier you are. (Highly skilled skiers can control a shorter ski, which will enable them to go faster.) Terry Jones, an official with Water Ski and Wakeboard Canada, offers a handy chart that shows you how to choose a ski based on both your body weight and the speed that you intend to ski. A 160-pound (72.5-kilogram) skier, for example, should go for a 67- or 68-inch (170- to 172.7-centimeter) ski if he or she will be skiing at a slow 26 miles per hour (41.8 kph). A skier of the same size but with the skill to ski 10 miles per hour (16 kph) faster, in comparison, should opt for a 65 or 66-inch (165- or 167.64-centimeter) ski [source: Terry Jones].
Pay attention to the shape, too. Slalom skis for weekend and vacation skiers have wider tails and flatter bottoms, and the high-performance models that the pros use have narrower, tapered tails, concave bottoms and highly beveled edges [source: Smith].
Trick water skiing and jumping also require different types of skis. Trick skis are shorter, more maneuverable versions of combo skis, while jump skis are longer and wider, to make it easier for a jumper to land on his or her feet [source: Smith]. But if you're a beginner, it'll be a while before you have to worry about shopping for either of those types of skis.