Ideal body weight and lean body mass sound like the same idea, and the two terms were historically conflated — but the calculators answer different questions with different formulas. Ideal body weight is a weight-for-height estimate: one number for one height and sex, derived from the Devine formula that began as a clinical drug-dosing reference. Lean body mass is a body-composition estimate: the weight of everything except fat, derived from the Boer equations and then turned into fat mass and body fat percentage.
Both pages on this site explicitly call out the distinction, because mixing the two concepts up is one of the most common ways these tools are misread. This page compares them so the choice is clear. It is informational, not medical advice, and neither number is a health verdict.
What each calculator does
The ideal body weight calculator needs your sex and height. It applies the Devine formula — men 50 kg at 5 feet plus 2.3 kg per inch over 5 feet, women 45.5 kg plus 2.3 kg per inch over 5 feet — and also shows the healthy weight band for your height (the weights producing a BMI of 18.5 to 24.9). For a 180 cm man it returns 75.0 kg, with a healthy weight band of 59.9–80.7 kg. The page is explicit that the Devine number is a dosing heuristic from 1974, not a weight-loss target.
The lean body mass calculator needs sex, height, and weight. It applies the Boer 1984 equations — men , women — then derives fat mass (weight minus lean mass) and body fat percentage. For a 175 cm, 70 kg man it shows 56.0 kg of lean mass, 14.0 kg of fat mass, and 20.0% body fat. The page stresses that the equation assumes average body composition and is a rough approximation for very muscular or otherwise atypical bodies.
Side-by-side comparison
| Feature | Ideal body weight calculator | Lean body mass calculator |
|---|---|---|
| Inputs | Sex and height | Sex, height, and weight |
| Primary result | Devine ideal body weight | Lean body mass (Boer) |
| Secondary results | Healthy weight band (BMI 18.5–24.9) for your height | Fat mass and body fat percentage |
| Formula basis | Devine 1974: base weight plus 2.3 kg per inch over 5 ft | Boer 1984: height-and-weight equations, sex-specific |
| Origin | Drug-dosing heuristic | Body-fluid normalization research |
| What it cannot show | Body composition, muscle, frame size | Direct measurement of tissue; assumes average composition |
| Example | 180 cm man: 75.0 kg, band 59.9–80.7 kg | 175 cm, 70 kg man: 56.0 kg lean, 14.0 kg fat, 20.0% body fat |
When to use which
Use the ideal body weight calculator when your question is weight-for-height in the dosing sense: the Devine reference number, how it compares with the BMI healthy weight band at your height, or which height-based convention a clinical protocol might use. It needs only sex and height, and it is honest that a single “ideal” number is a decades-old heuristic.
Use the lean body mass calculator when your question is composition: how much of your weight might be lean tissue versus fat, or a body fat percentage derived from height and weight without any tape measure or calipers. It needs your weight, and it gives you the fat-versus-lean split directly.
For a fuller picture, either number benefits from companions: the BMI calculator puts weight in a height-relative screening context, the body fat calculator uses tape-measure inputs instead of height and weight only, and the BMR calculator turns the same inputs into energy estimates. If your results from different tools disagree, that is expected — different formulas and different measurement demands — not a sign that one tool is broken.
Where to start
- Ideal body weight calculator — Devine weight-for-height estimate with the BMI healthy weight band.
- Lean body mass calculator — Boer lean mass estimate with derived fat mass and body fat percentage.
Informational note: This page is an educational comparison, not medical advice. Ideal body weight is a historical dosing heuristic, and lean body mass from height and weight is an equation estimate that assumes average body composition — neither measures your body directly, and neither is a health verdict or a weight goal. Discuss weight or body-composition goals with a qualified healthcare professional.