Your ideal weight is not a single number but a range — a healthy zone where your weight supports long-term wellbeing without the health risks of either underweight or excess body fat. An ideal weight calculator estimates that range from your height and sex, giving you a practical target whether you are planning weight loss, weight gain, or simply confirming you are in a healthy place.
Ideal-weight estimates are derived from population-based equations — commonly the Devine, Robinson, Miller, and Hamwi formulas — each producing slightly different numbers. The real value is not the precision of any one equation but the range they define, which health professionals broadly agree represents a sensible target for most adults.
How Ideal Weight Is Estimated
The classic equations estimate ideal weight from height and sex. The Devine formula (used in most medical dosing contexts) gives men 50 kg + 2.3 kg per inch over 5 feet, and women 45.5 kg + 2.3 kg per inch over 5 feet. The Hamwi, Miller, and Robinson formulas each vary slightly in base weight and increments.
For a 5'9" (175 cm) man: Devine gives 50 + 2.3 × 9 = 70.7 kg (about 156 lb). For a 5'5" (165 cm) woman: 45.5 + 2.3 × 5 = 57 kg (about 126 lb). The formulas converge on similar target ranges, and physicians commonly present ideal weight as a zone spanning roughly 5-10 kg around the formula result.
Height-based approaches have limitations: they assume average frame size and average muscle proportions. A tall, broad-shouldered individual will naturally carry a slightly higher healthy weight than the equations suggest, and athletes exceed them legitimately because of lean mass. Use the range as guidance, not a verdict.
Linking Ideal Weight and BMI
The healthiest approach cross-references ideal-weight equations with BMI: the normal-weight BMI zone (18.5-24.9) defines weight ranges by height. For 5'9", the normal BMI range spans about 125-169 lb — the ideal-weight formulas land near the middle of that healthy band.
What matters for health is staying within a healthy range relative to your height, not chasing a precise pound figure. The risks of being significantly outside the range — metabolic syndrome, cardiovascular disease, diabetes, joint problems, sleep apnea, and impaired fertility on the high side; malnutrition, bone loss, and weakened immunity on the low side — all scale with distance from the healthy zone.
A useful refinement: rather than ideal weight alone, track body composition. A person at the top of the ideal-weight range with muscle and low body fat is healthier than someone at the bottom with high fat. Ideal weight is a screening target; waist circumference and body fat percentage confirm the composition inside the number.
Practical Targeting: Gain, Lose, or Maintain
If your current weight is above your ideal range, set a realistic staged target: the top of your healthy range first (a manageable 5-10% reduction), reassess, then continue. Losing 1-2 lb per week is sustainable and preserves muscle with adequate protein and strength training.
If you are below the healthy range, the focus should shift to ensuring adequate caloric intake and lean mass — especially for athletes and older adults, where gaining a few pounds of muscle meaningfully improves health and resilience. Both directions benefit from monitoring waist circumference alongside weight.
Best practice is bringing the calculator's number into your routine, not your identity: weigh in on a consistent schedule, use trend over single measures, and adjust intake by real-world results. Ideal weight is a compass for habit, not a scorecard for self-criticism.
Ideal weight is best understood as a healthy range, not a fixed verdict. Calculate yours from your height, keep the range framed by BMI, and layer in body composition to personalize the target. Whatever direction you are heading — down, up, or holding steady — measure trends consistently, move slowly and sustainably, and let the healthy zone guide habits rather than define self-worth.