The general rule of thumb to go by would be to find a grip that is most suitable for the individual as it is not a one size fit all kind of concept. The grip will not only determine the quality of play that the player eventually displays but can also affect the body conditions negatively.
Basically it would be better to start with a smaller grip size and then make adjustments until the grip size is both comfortable and safe for the user. If the grip used is unsuitable, there would be some twisting of the hand to, execute the stoke each time it is executed, thus contributing to the tennis elbow syndrome. This is a rather painful condition and would almost always require the attention of a medical professional.
The ideal grip size is usually found anywhere between the standard measurements of 4” to 4 and 5/8” and are at about 1/8” in intervals. The grip is often calculated by referring to the circumference of the grip the individual makes when holding the racquet. In order to get an estimation of the most appropriate grip size, a ruler should be placed at the bottom of the horizontal crease in the palm of the hand that is going to be holding the racquet. The measurement is taken from this point to the tip of the ring finger. This will indicate the ideal grip size for the individual. However if there is a need, and additional over grip can the added on which is about 1/16” in size to make the feel more comfortable.
Another method for measuring the grip would be to observe the amount of space between the fleshy part of the pal, and fingertips. Being able to “plug” this gap with the index finger of the other hand comfortably without any looseness or tightness (that doesn’t allow the finger in), would then give the player a good idea of the suitability of the grip chosen.