The difference in 5 sq ins and the import some players here put on it is amusing. If it isn't broke, don't fix it.
If you find a personal racket of a player you want to check then you might follow this....
To approximate the area by treating it as if the tennis racquet head were an oval or an "ellipse" for which there is an area formula: A= \pi ab where a and b are half the distance across the racquet head measured where it is narrowest and widest.
In other words, you are really using the formula for area of a circle, but, because an "ellipse" does not have a single "radius", instead of r2, you multiply together the values for smallest "radius" and largest "radius".