The standard guidelines for age and racquet size are charted below, but you should adjust for several additional factors. If an 8-year-old is the size of an average 10-year-old, choose for a 10-year-old. You should move up one size, possibly two, to adjust for exceptionally high physical strength, but adjusting down for lack of strength is almost never necessary. Modern junior racquets are extremely light, and even a total couch potato should be able to wield the racquet designed for her age. Experience is also a factor. The chart assumes a beginner player. An experienced player will often do best with a size or two larger than the chart indicates. Experienced players will have enough feel for their strokes to be able to conduct a meaningful demo.
Age: Racquet Length
0-4: 19"
4-5: 21"
6-7: 23"
8-10: 25"
10-12: 26"
12 up: adult size
You will notice overlaps in the above chart at ages 4, 10, and 12. At these ages, either size is equally likely to be suitable, but as a general rule, when in doubt, go with the bigger racquet.
If a junior is just barely big enough for an adult racquet, he's probably better off with a standard 27" racquet than with an extra-long. Despite all of the recent advances in reducing the swing weight of extra-long racquets, they still tend to play heavier than shorter racquets of the same weight.
Adult racquets come as light as 8 ounces these days, but racquets lighter than 10 ounces start approaching too small a multiple of the weight of the ball. I find that an average 12-year-old hits quite comfortably with a racquet weighing 10-11.5 ounces.
Beginners won't have enough feel for tennis strokes to be able to make a firm decision based on an on-court demo, but if a junior is completely torn between two sizes of racquets, here's a test that might help him decide. Have him hold the racquet behind him so that the tip touches his lower back and his elbow is the highest part of his arm. Have him raise the racquet overhead, much as if he were serving, but with a slow swing. If the racquet is going to be too heavy for him, this is where he'll feel it.
Juniors can outgrow racquets quickly, but it helps a lot that junior racquets tend to be inexpensive. Very nice junior racquets at a pro shop will run roughly $20 to $50, and some of the $10 racquets at the big discount chains are quite good, too. When you look at the least expensive racquets, one crude test is to bang the strings on the butt of your hand to get a feel for their solidity. Avoid racquets that seem lighter or more flexible than the others in the bottom end of the price range.
