The Donoghue formula works well for calculating expected weights for your tortoise given their size(s). You can then conduct a Body Mass Index (BMI) from what the formula states the tortoise should weigh versus what it's actual weight is. This works best for larger tortoises, not hatchlings. The tortoise library has an excellent discussion on this (http://tortoiselibrary.com/ - "healthy weight and size") and Madkins007 has a great thread concerning this: http://www.tortoiseforum.org/Thread-Tortoise-Weight-Formula-tBMI#axzz22LkDTHTr