The Problem with "Ideal" Weight
The concept of an "ideal" weight is somewhat misleading. No single number fits everyone, and the weight that looks best on you depends on factors unique to your body, including bone density, muscle mass, fat distribution, and personal preferences. Treating a calculator result as gospel truth misses the point entirely.
These formulas were mostly developed for medical and pharmaceutical purposes. The Devine formula, for instance, was created in 1974 to estimate ideal body weight for drug dosing calculations. Using it as a fitness target ignores its original clinical context. You can calculate your ideal weight using our ideal weight calculator.
Major Formula Approaches
The Devine Formula, also called the Devine Index, was developed by Dr. B.J. Devine primarily for calculating drug dosages. For men: 50 + 2.3 kg per inch over 5 feet. For women: 45.5 + 2.3 kg per inch over 5 feet. This formula tends to produce lower "ideal" weights and is most accurate for people of average height.
The Hamwi Formula from 1964 uses slightly different coefficients. Men get 48 kg for 5 feet plus 2.7 kg per inch above that; women get 45.5 kg plus 2.2 kg per inch. This tends to give higher results than Devine for taller individuals.
A 5'10" man using Devine gets approximately 75 kg (165 lbs). The same man using Hamwi gets roughly 78 kg (172 lbs). Neither is definitively correct — they're just different mathematical approaches to an inherently imprecise concept.
BMI-based ranges provide another approach, targeting the middle of the "normal" BMI range (18.5-24.9). For someone 5'10", this translates to roughly 62-83 kg (137-183 lbs). The range itself is wider than any single-number formula, acknowledging the individual variation that a single "ideal" ignores.
Why Body Composition Matters More Than Weight
A 180-pound person with 25% body fat looks dramatically different from a 180-pound person with 12% body fat. Same weight, completely different bodies. This is why fixating on scale weight without considering composition leads to frustration and poor decision-making.
Two people can wear the same clothing size but differ by 20 pounds purely due to muscle density differences. A muscular person may be "overweight" by BMI standards while having very low body fat. Conversely, a normal-weight person with minimal muscle might carry dangerous visceral fat.
The practical question isn't "what should I weigh?" but rather "what body composition do I want?" Knowing your target body fat percentage gives you something more actionable to pursue. A man might aim for 15% body fat; a woman for 22%. These targets reflect aesthetic and health goals that actually matter.
Setting Realistic Goals
Healthy weight loss typically ranges from 0.5 to 1 kg (1-2 lbs) per week. Faster rates usually indicate water loss or muscle loss rather than fat loss, which isn't sustainable. If you have 20 kg to lose, expect it to take 5-6 months minimum for meaningful results.
Consider strength improvements, energy levels, and how your clothes fit as additional success markers beyond the scale. Someone who loses 5 kg of fat but gains 3 kg of muscle over three months might see the scale barely move while looking dramatically different.
Set process goals rather than purely outcome goals. "Exercise 4 times per week" and "eat protein with every meal" are actionable and controllable. "Weigh X pounds by summer" depends on factors beyond your control and sets you up for frustration if the timeline doesn't match reality.