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Body Fat Calculator — US Units (lb/in)
Estimate your body fat percentage with the Deurenberg BMI-derived formula. Defaults to US imperial units for weight (lb) and height (in). Real-time update as you type.
How the Deurenberg Formula Works
Published in 1991 by Deurenberg, Weststrate, and Seidell, the formula estimates body fat percentage from three easily measured inputs: BMI, age, and gender. It was derived via regression analysis using hydrostatic weighing (underwater weighing) as the criterion body composition method in a combined Dutch and New York adult dataset.
Formula
Body Fat % = 1.2 × BMI + 0.23 × age − 10.8 × gender − 5.4
Where gender = 1 for males, 0 for females. The BMI is computed from your weight and height using the standard formula (703 × lb / in² for imperial units, or kg / m² for metric).
What the coefficients mean
The 1.2 coefficient scales BMI into the approximate body-fat-percentage domain. The 0.23 age coefficient captures the population-level trend that body fat % rises with age at constant BMI, largely due to sarcopenic shifts (loss of lean mass, gain of fat mass). The 10.8 gender coefficient reflects the average body fat percentage difference between males and females at the same BMI and age. The −5.4 intercept anchors the equation to the hydrostatic weighing reference scale.
Healthy Body Fat Percentage by Age and Gender
Body fat percentage that is considered "healthy" is not a single number — it shifts upward with age and is systematically higher for women than for men. The age-adjusted reference bands below come from the body-composition norms published by Gallagher et al. (2000, American Journal of Clinical Nutrition) and Jackson et al. (2002, International Journal of Obesity), which are the most widely cited age-adjusted adult reference ranges in North American clinical and fitness practice.
| Age Group | Men — Healthy Range | Women — Healthy Range | Men — Overweight Threshold | Women — Overweight Threshold |
|---|---|---|---|---|
| 20–29 | 8 – 19% | 17 – 26% | > 19% | > 26% |
| 30–39 | 11 – 21% | 18 – 27% | > 21% | > 27% |
| 40–49 | 13 – 23% | 19 – 28% | > 23% | > 28% |
| 50–59 | 14 – 24% | 20 – 29% | > 24% | > 29% |
| 60+ | 15 – 25% | 21 – 30% | > 25% | > 30% |
Two patterns matter. First, the healthy band rises by roughly 1 percentage point per decade for both sexes — this reflects the sarcopenic drift the Deurenberg formula captures with its 0.23 × age coefficient. Second, women carry about 8–10 percentage points more body fat than men at every age, which is driven by sex-specific physiology and the 10.8 gender coefficient in the Deurenberg equation. A 45-year-old man at 22% body fat is comfortably inside the healthy band; a 45-year-old woman at 22% is also healthy, but sits lower in her band because her reference ceiling is higher.
For athletes, the bands below the "healthy" floor still apply: the ACE athlete ranges (6–13% men, 14–20% women) describe competitive training levels, not targets for the general public. Going below essential fat (2–5% men, 10–13% women) is a clinical concern, not a fitness goal.
ACE Body Fat Reference Ranges
The American Council on Exercise (ACE) publishes widely used practitioner reference bands for body fat percentage. These ranges are population-level reference points, not diagnostic thresholds.
| Category | Men | Women |
|---|---|---|
| Essential Fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Acceptable | 18–24% | 25–31% |
| Obese (≥ threshold) | ≥ 25% | ≥ 32% |
Interpreting Your Body Fat Estimate
The Deurenberg formula is a population regression, not a direct measurement. Prediction errors of 3–5 percentage points relative to gold-standard multi-component methods (DXA, underwater weighing, deuterium dilution) are typical. Individuals with high muscle mass may receive overestimates because BMI does not partition lean from fat mass. Conversely, older adults with reduced lean mass may receive underestimates. Results labeled "Essential Fat" represent the minimum physiological fat required for endocrine and structural function, not a recommended target. For clinical assessment, consult a qualified healthcare provider.
Body fat percentage works best alongside your BMI and your TDEE. BMI tells you where you sit on the population weight-to-height scale; body fat % tells you how much of that weight is adipose tissue; TDEE tells you how many calories you actually burn. Read the three together and you have a much clearer picture than any single number can give.