Here is the size chart for choosing Watery Remington Girls' Rashguard. This rashguard is based on chest, hip, bottom line, sleeve length, wrist, and torso measurements to find your correct size.
If you are unlucky and find yourself between two sizes, choose the one that is closest or according to your preferred fit. Additionally, consider the fit you desire; for a tight fit, choose the smaller of the two sizes, alternatively, choose the larger of the two sizes if you prefer a looser fit.