Body Composition
What’s Your Ideal Body Weight? (And Why the Number Lies)
Old formulas spit out a single number based on your height and sex. That number ignores how much muscle you carry, your age, your frame, and what you actually look and feel like. Here’s what those formulas say, what they can’t tell you, and why body composition is the better target.
The classic formulas
Three formulas dominate discussions of ideal body weight in clinical and popular health literature: Devine (1974), Robinson (1983), and Hamwi (1964). All three estimate a single target weight from height and sex. None of them were designed with athletes or body composition goals in mind — they were originally used for calculating drug doses in hospitals, where lean body mass matters more than total weight.
| Formula | Men (base + per inch over 5 ft) | Women (base + per inch over 5 ft) |
|---|---|---|
| Devine | 50 kg + 2.3 kg/in | 45.5 kg + 2.3 kg/in |
| Robinson | 52 kg + 1.9 kg/in | 49 kg + 1.7 kg/in |
| Hamwi | 48 kg + 2.7 kg/in | 45.5 kg + 2.2 kg/in |
To use the Devine formula for a 5’10” man: 50 + (10 × 2.3) = 73 kg, or roughly 161 lb. By Robinson, the same person gets 52 + (10 × 1.9) = 71 kg (156 lb). The three formulas give similar outputs but not identical ones, and the spread grows for taller or shorter people.
These estimates are a useful starting reference, but they share a fundamental problem: they assume everyone of the same height and sex has the same muscle-to-fat ratio. A heavily muscled powerlifter and a sedentary office worker of the same height will both get the same “ideal” number from these formulas, even though their body compositions — and health pictures — could not be more different.
If a formula suggests your ideal weight is 155 lb and you currently weigh 185 lb with significant muscle mass, the formula is not useful guidance. It was not built for you.
BMI and its limits
Body Mass Index — weight in kilograms divided by height in meters squared — is the most widely used population-level weight classification tool. The standard categories run from underweight (below 18.5) through normal (18.5 to 24.9), overweight (25 to 29.9), and obese (30+).
At the population level, BMI correlates reasonably well with body-fat percentage and health risk. For screening large groups, it is fast and costs nothing. The problem is applying it to individuals.
BMI cannot distinguish muscle from fat. A person carrying 20 lb more muscle than average at the same height will be classified as overweight or obese by BMI despite a healthy body composition. Conversely, a person who is “normal weight” by BMI but has lost significant muscle mass with age (a condition sometimes called skinny fat) can carry a high body-fat percentage with elevated metabolic risk that BMI misses entirely.
BMI also does not account for where fat is stored. Visceral fat — the fat packed around abdominal organs — is far more metabolically harmful than subcutaneous fat stored under the skin. Two people with identical BMIs can have very different visceral fat distributions and corresponding health risks.
Why scale weight misleads
The scale measures total mass: fat, muscle, bone, water, food in transit, and everything else. Two people can weigh exactly the same and look completely different, have completely different health profiles, and require completely different calorie targets.
| Person A | Person B | |
|---|---|---|
| Scale weight | 170 lb | 170 lb |
| Body fat % | 15% | 30% |
| Fat mass | ~26 lb | ~51 lb |
| Lean mass | ~144 lb | ~119 lb |
| TDEE (approx.) | ~2,300 kcal | ~1,950 kcal |
| Appearance | Lean, visible muscle | Soft, low muscle tone |
Person A and Person B weigh identically. But Person A carries 25 lb more muscle, burns roughly 350 more calories per day at the same activity level, and has a meaningfully lower health risk profile. No scale number captures this difference — only body composition does.
This is why chasing a specific weight target — whether from an ideal body weight formula or a round number you have in mind — can lead you to the wrong goal. If you lose 20 lb by dieting alone, without resistance training or adequate protein, a significant portion of that loss will be muscle. You might hit the formula’s recommended number while looking and feeling worse than a lighter-training approach would leave you.
Measure what actually matters
Your body-fat percentage tells you far more than your scale weight. Use the body fat calculator to estimate where you stand — and where you want to go.
Check my body fat %Body fat: the better lens
Body-fat percentage expresses how much of your total weight is fat versus lean mass (muscle, bone, water, organs). It is the metric that actually captures what ideal weight formulas are trying to approximate.
Several methods can estimate it. The body fat calculator uses either the Navy tape method (neck, waist, and hip circumferences) or a BMI-adjusted estimate. Both are approximate but give a meaningful starting point without equipment. For more accuracy, a DEXA scan is the practical gold standard — a 10-minute scan provides a detailed breakdown of fat, muscle, and bone density by region. Skinfold calipers and hydrostatic weighing are also reasonably accurate in skilled hands but less accessible.
No method is perfect. Consumer bioimpedance scales (the kind with handheld electrodes or foot sensors) are notoriously inconsistent and can swing 3 to 5 percentage points based on hydration alone. Use any single measurement as a directional reference and track changes over time rather than fixating on the absolute number.
Healthy body-fat ranges
The ranges below reflect broadly accepted health and fitness guidelines. They are not strict rules; individual health depends on many factors beyond body fat alone. Consider them starting targets for orientation rather than finish lines.
| Category | Men | Women |
|---|---|---|
| Essential fat (minimum) | 3–5% | 10–13% |
| Athlete | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Acceptable / average | 18–24% | 25–31% |
| Overweight / obese territory | 25%+ | 32%+ |
Women carry higher essential fat than men because reproductive hormones require it. The “athlete” range reflects the low end seen in lean, competitive athletes and is not a health requirement for most people. Most healthy, fit, non-athlete adults land comfortably in the fitness to acceptable range.
Dropping below essential fat levels disrupts hormonal function, bone density, immune response, and cardiovascular health. “Lean as possible” is not the goal; “lean enough to be healthy and perform well” is. See the guide on calculating body fat percentage for a full breakdown of measurement methods.
What to actually aim for
Instead of targeting a specific scale weight, most people benefit from working toward a body-fat percentage within the healthy range for their sex, a waist circumference associated with lower metabolic risk, and a level of physical capability and energy they can sustain.
Practically, that means two things: a calorie approach that produces a modest deficit if fat loss is the goal, and a training approach that builds or protects muscle while you lose. Use the TDEE calculator to establish your maintenance calories, then set a 250 to 500 calorie daily deficit for a sustainable fat-loss pace of roughly 0.5 to 1 pound per week. Use the cutting calculator to get a specific target if you’re focused on fat loss.
If your goal is to change your body composition without necessarily losing much scale weight — gaining muscle while losing fat — that is body recomposition, a different goal entirely. The scale will not show the progress, but photos, measurements, and how your clothes fit will.
A body-fat percentage in a healthy range, a waist you can maintain, and the strength and energy to live the way you want. Those are better targets than any number on a scale or formula output.
Frequently asked questions
What is ideal body weight?
Ideal body weight is a target weight range associated with good health outcomes, typically estimated from height, sex, and sometimes frame size. Classic formulas like Devine and Robinson give a single number, but health researchers increasingly prefer body-fat percentage and waist circumference as more informative markers because scale weight does not distinguish muscle from fat.
How do I calculate my ideal body weight?
The most common formula for men is the Devine formula: 50 kg plus 2.3 kg for every inch over 5 feet. For women it is 45.5 kg plus 2.3 kg per inch over 5 feet. These were originally developed for drug dosing in clinical settings, not fitness goals, so treat the output as a rough reference rather than a precise personal target.
Is BMI a reliable indicator of ideal body weight?
BMI is a useful population-level screening tool but a poor individual measure. It cannot distinguish between muscle and fat, so muscular people frequently appear overweight by BMI while sedentary people with high body fat can appear in the normal range. It also does not account for age, sex differences in body composition, or ethnic variation in risk thresholds.
What body-fat percentage should I aim for?
For general health, men typically aim for 10 to 20% body fat and women for 18 to 28%. Athletes often carry less. Essential fat — the minimum needed for organ function and hormones — is roughly 3 to 5% for men and 10 to 13% for women. Going below essential fat levels is dangerous. These ranges are guidelines, not strict rules, and individual health factors matter.
Can two people weigh the same but have very different body compositions?
Yes, and this is precisely why scale weight is an incomplete metric. A 170 lb person who is 15% body fat carries roughly 26 lb of fat and 144 lb of lean mass. A 170 lb person at 30% body fat carries 51 lb of fat and 119 lb of lean mass. They weigh identically but have very different health profiles, appearances, and calorie-burning capacity.
What is a healthy waist circumference?
As a general guideline, waist circumference below 40 inches for men and 35 inches for women is associated with lower cardiovascular risk. Waist-to-height ratio below 0.5 is another commonly cited healthy range. These measurements correlate with visceral fat, which is the metabolically active fat stored around the organs, and are considered more predictive of metabolic risk than BMI alone.
Do ideal body weight formulas apply to everyone?
No. The classic formulas were developed from clinical datasets that skew toward specific populations and were designed for medication dosing, not health optimization. They assume a single body composition for a given height, which is unrealistic. Muscular individuals, older adults who have lost muscle mass, and people with different bone densities will all get misleading outputs from these formulas.