Numbers are used all the time in the lactation field. Test weights, percentiles, % of weight gain, are just some of the information that is gathered to help make infant feeding decisions. But what are they really telling us? When are they useful? Using these numbers in a way that actually helps support and promotes breastfeeding are key. Appropriate infant weight gain, how to do a test weight, scale calibration, calculating infant intake, and the possible need for supplementation, will all be covered.