To start with, you should purchase a jump rope in an appropriate length and then adjust the size from there. Generally, start with a jump rope in the lengths outlined in this sizing chart:
|Length of Rope||Height|
|7 feet||Shorter than 5' 2"|
|8'||5'2" - 5' 6"|
|9'||5' 6" - 6' 2"|
|10'||6' 3" - 6' 7"|
Form & Sizing Method
Because of the variance in the length of the people's legs, arms, and torso, a generic sizing method doesn't work perfectly. Rather, when I size a jumper, I look at how high the jump rope is over the head while jumping. For any sizing method to work, it is very important that the jumper is using proper form. Most importantly, the hands are just in front of the hip bones and not held out wide when jumping. If there is nobody to watch you, a reflection in a mirror provides you with the height.
Because speed is not the objective, a longer rope is ideal for children and beginners. A longer jump rope slows things down and allows for timing that is not perfect.
How to size: Stand on the jump rope in the middle of the cord with both feet. The BOTTOM of the jump rope handles should come up to the armpit.
Correct sizing: The rope/cable clears 6" to 10" over your head at its apex when jumping.
When I observe people jumping rope in the gym or doing double unders for CrossFit, it is typical to see the cable 12" to 36 " over their heads. For fitness workouts this rope length is much too long (for most people), and is really slowing them down. My suggestion for fitness workouts and double unders would be to size the jump rope so that it is traveling over the head by 6"-10". I do not hold tight to this rule because there are so many great jumpers that use a variable of different heights. It needs to be a height that you are comfortable with. The idea is to get the rope turning around your body with as little effort as possible with maximum rope control. A jump rope that is too long will be sloppy and take too much effort to turn.
Correct sizing: The cable clears 2" to 6" over your head at its apex when jumping.
It is all about speed and control. Going as fast as you can without making mistakes. Going 6-7 jumps a second takes great strength, endurance, and control of the jump rope. Typically the fastest jumpers in the world have the cable 2" to 6" over their head (some even down to 1"). They typically crouch down to make the circumference traveled by the jump rope even smaller.
Correct sizing: The rope clears 12" to 24" over your head at its apex when jumping.
Doing jump rope tricks is all about placing the handles of the jump rope in the right place at the right time. For this to happen, it is best to use a jump rope that will give the jumper the most control over the rope. For freestyle, the correct length is whatever the jumper is most comfortable with. Typically the jump rope will be 12" to 24" over their heads. However it is not uncommon to see the ropes only a few inches the head of many competitive freestyle jumpers. There is more variation in jump rope sizing for freestyle than any other type of jumping.