When making an investment in new tennis racquet there is a lot of information to sift through. Perhaps nothing is as important as getting the correct size handle.
The 1st measuring method below you can use measuring tape or a ruler, whichever you may have on hand (pun intended). Find the crease that runs across your hand and place the measuring tape/ruler as shown below. You are measuring the tape from the crease to the end of your ring finger. Below would be in between 4 ¼ (Grip Size 2) and 4 3/8 (Grip Size 3)
If you have a racquet handy (pun intended) but no measuring tool, here is another good way to get an estimated grip size. Pick up the racquet in a “hand shake” grip, if you can place your other index finger in the space between thumb and fingers then that grip size is probably a good place to start.
Here is the same measuring example but on a handle size that is way too small. Note there is no space for the index finger at all. Also note how tight the fingers are having to squeeze to keep a firm grip. This can lead to fatigue in the wrist and perhaps the ever awful tennis elbow.
Keep in mind these measurements are meant to give you a baseline and help you decide a good place to start. Some experienced players prefer a grip slightly smaller or larger than a measurement would show.
Pro tip: On volleys, and when powerful shots are directed your way, a grip that is too small can twist in the hand and you can lose confidence quickly in your grip. If the grip is too large it can be difficult to switch to different grips during play.
Ideally you want the best of both worlds and there is some margin of error so when in doubt, go with what is comfortable to you. And remember if you feel “in-between” grips sizes, go with the smaller one because it’s easy to build it up if need be.
You can use overgrip to increase the grip size.