The Problem With "Ideal Weight"
Type "ideal weight calculator" into any search engine and you will be presented with dozens of tools, each confidently returning a specific number. Yet ask four different tools about the ideal weight for a 175cm woman and you will likely receive four different answers, potentially varying by 10 kilograms or more. Ask a doctor, a nutritionist, and a sports scientist the same question and you will receive three different frameworks, each emphasising different factors.
The concept of an "ideal weight" is more complicated than it appears — and more personal. This guide explains how ideal weight is calculated, why different formulas produce different answers, and why the most meaningful measure of whether you are at a healthy weight is not a single target number at all.
A Brief History of Ideal Weight Formulas
The idea of a target body weight based on height was developed primarily for clinical and insurance purposes — not for individual health optimisation. Several formulas from the 1960s and 1970s remain in widespread use today, each developed from population data of the era with somewhat different methodologies.
The Devine Formula (1974)
The Devine formula was originally developed to guide drug dosing in clinical settings — specifically to calculate appropriate medication doses based on lean body mass rather than total body weight. It was never intended as a general health or fitness target. Despite this, it became widely adopted as an "ideal body weight" reference.
- Men: IBW = 50 kg + 2.3 kg × (height in inches above 5 feet)
- Women: IBW = 45.5 kg + 2.3 kg × (height in inches above 5 feet)
For a 175cm (5 foot 9 inch) man, Devine gives approximately 70.9kg. For a 165cm (5 foot 5 inch) woman, approximately 57.3kg. These values represent relatively lean body weights and may be unrealistically low for heavily muscled individuals.
The Robinson Formula (1983)
Robinson and colleagues revised Devine's formula to better reflect average population weights at the time:
- Men: IBW = 52 kg + 1.9 kg × (height in inches above 5 feet)
- Women: IBW = 49 kg + 1.7 kg × (height in inches above 5 feet)
The Hamwi Formula (1964)
The Hamwi formula was developed for clinical practice and uses slightly different base weights and increments. It tends to produce higher ideal weight values than Devine or Robinson, particularly for shorter individuals.
The Miller Formula (1983)
The Miller formula produces the lowest ideal weight estimates of the common formulas and is generally considered to represent very lean body weights that most healthy adults would struggle to maintain without significant effort.
Why the Formulas Give Different Answers
Each formula was derived from different population datasets, different time periods, and different definitions of "ideal." None of them accounts for individual variation in muscle mass, bone density, frame size, age, or ethnicity — yet these factors profoundly influence what a healthy weight looks like for any given individual.
A 175cm man who is a competitive runner with 10% body fat might weigh 68kg. A 175cm man who is a powerlifter with 15% body fat and significant muscle mass might weigh 90kg. Both could be at genuinely healthy body compositions for their activity and goals — yet the standard formulas would describe only the runner as being at "ideal weight" and label the powerlifter as significantly overweight.
This illustrates why single-number ideal weight targets are an imperfect tool: they do not measure what actually matters, which is body composition — the proportion of your weight that is muscle, fat, bone, and other tissues.
BMI as an Alternative Framework
The Body Mass Index (BMI) provides a range rather than a single target, which partly addresses the problem of single-number ideal weights. The BMI "normal weight" range of 18.5 to 24.9 translates to a range of weights for any given height:
For a 175cm person: Normal weight BMI range = 18.5 to 24.9 = approximately 56.6kg to 76.2kg. This is a range of nearly 20 kilograms, acknowledging that a single "ideal" weight for all people of a given height is not realistic.
However, BMI has its own well-documented limitations. It cannot distinguish between fat mass and muscle mass, does not account for fat distribution, and uses cut-offs calibrated primarily on European populations. A heavily muscled person can have a BMI in the "overweight" category with a body fat percentage in the athletic range. Conversely, a person with a normal BMI but very little muscle can have an unhealthily high body fat percentage — a condition sometimes called "skinny fat" or normal-weight obesity.
Frame Size and Its Effect on Ideal Weight
Some older approaches to ideal weight incorporated frame size — small, medium, or large — to acknowledge that people of the same height naturally have different skeletal structures. A person with large wrist bones, wide hips, and broad shoulders simply has more bone mass than someone with the same height but a lighter frame.
Frame size can be estimated using wrist circumference relative to height, or by wrapping your thumb and middle finger around your wrist: if the fingers overlap, you likely have a small frame; if they just meet, a medium frame; if there is a gap, a large frame.
Large-framed people naturally weigh more than small-framed people of identical height even at the same body fat percentage. Adding a frame size adjustment to ideal weight calculations produces more realistic targets than height-alone formulas, though it still does not account for individual muscle mass variation.
What a Truly Healthy Weight Looks Like
Rather than fixating on a specific target weight derived from a formula, a more meaningful approach to defining a healthy weight involves considering multiple factors together:
- Body fat percentage within healthy ranges. For men, 10 to 20% body fat is broadly associated with good health and physical function. For women, 20 to 30%. These ranges are wide enough to accommodate different body types and activity levels while remaining within health-supporting territory.
- Waist circumference below threshold values. A waist circumference above 102cm (40 inches) for men or 88cm (35 inches) for women is associated with elevated cardiometabolic risk regardless of total body weight. This directly measures central adiposity — a better predictor of metabolic health risk than total body fat.
- Normal metabolic blood markers. Fasting glucose, HbA1c, fasting insulin, triglycerides, HDL and LDL cholesterol, and blood pressure together provide a comprehensive picture of metabolic health that no weight measurement can match.
- Functional physical capacity. The ability to move freely, perform daily activities without excessive effort, and maintain adequate strength and cardiovascular fitness for your age is a practical health metric that is often more meaningful than any number on a scale.
- Weight that is stable without excessive effort. A weight you can maintain with sustainable eating habits and reasonable activity levels, without chronic restriction, is generally a healthier target than a formula-derived number that requires constant struggle to achieve or maintain.
Setting a Realistic Personal Target
If you want a practical starting point for a weight goal, use a range rather than a single number. The healthiest approach for most people:
- Calculate your BMI healthy weight range (BMI 18.5 to 24.9) — this gives you a broad boundary of plausible target weights for your height.
- Estimate your body fat percentage using our Body Fat Calculator — this tells you whether your current weight is predominantly lean or fat.
- Use your ideal weight calculator result (our tool averages across the major formulas) as a single reference point, not a definitive target.
- Choose a target weight within the healthy BMI range that feels sustainable given your body type, muscle mass, and activity level.
- Track body fat percentage and waist circumference alongside body weight for a more complete view of progress.
The Psychological Dimension of Ideal Weight
It is worth acknowledging that ideal weight targets can become counterproductive when pursued in isolation, particularly for people with a history of disordered eating or exercise. A number on a calculator has no context — it does not know your medical history, your lifestyle, your relationship with food, or what weight allows you to live well.
Health at every size research consistently shows that health-promoting behaviours — adequate movement, nutrient-dense eating, sufficient sleep, stress management, and meaningful social connection — have measurable positive effects on health markers regardless of whether they result in weight loss. The pursuit of health behaviours is valuable even when weight does not change dramatically, and fixation on a target weight number can sometimes interfere with developing sustainable habits.
Conclusion
Ideal weight formulas provide a useful reference range but should not be treated as precise targets. They were derived from population averages and do not account for individual variation in muscle mass, frame size, age, or ethnicity. A more meaningful measure of whether you are at a healthy weight combines body fat percentage, waist circumference, metabolic blood markers, and functional capacity — not any single number from a calculator.
Use our free Ideal Weight Calculator to see what multiple formula approaches suggest for your height and sex, and use that range as a starting point for a personal, realistic goal.