These calculators use established medical formulas: BMI (kg/m²), Mifflin-St Jeor for daily calories, weight × 35 ml/kg for water intake, Devine formula for ideal weight, and standard macronutrient ratios (protein 2 g/kg, fat 25%, rest carbs). All tools support both metric (kg, cm) and imperial (lbs, ft/in, fl oz). US visitors auto-land on imperial; everyone else gets metric.