Theme > Kitchen has System Unit Weight (Metric vs Imperial) with options Lb / Kg, and System Unit Size (Metric vs Imperial) with Inchs / Centimeters. The weight unit is shown next to weight fields in the admin (meal net weight, bag types, and — when the FedEx integration is active — the shipping weight on a zip code/delivery zone) and on printed meal labels; the size unit is used for bag-type dimensions. Pick the units your kitchen works in; existing numbers are not converted automatically.