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Compare adult BMI (WHO categories) with a Deurenberg-style body fat % estimate from BMI, age, and sex. Optionally add measured body fat from a scale or lab to discuss agreement. Includes approximate fat and lean mass in kg—for teaching, not DEXA or clinical diagnosis. Pair with waist-to-height ratio.
Last updated: June 4, 2026
If provided (about 3–60%), fat mass uses measured %; otherwise it uses the regression estimate.
BMI
27
Overweight (25–29.9)
Est. body fat %
23.6%
Average range (male)
Fat mass (approx.)
18.4 kg
Lean mass (approx.)
59.6 kg
Comparison readout
Higher BMI with lower estimated body fat% — can occur with resistance training and larger lean mass. Regression estimates are often biased in athletes; prefer direct body composition testing if decisions depend on it.
Do not use this page to diagnose obesity or sarcopenia. Athletes, older adults, pregnancy, and many chronic conditions break simple BMI–body fat assumptions.
170 cm, 78 kg, male, 32 y
BMI 27
Overweight (25–29.9)
Est. fat ~23.6%
175 cm, 68 kg, male, 25 y
BMI 22.2
Est. fat ~16.2%
160 cm, 62 kg, female, 48 y
BMI 24.2
Est. fat ~34.7%
180 cm, 90 kg, male, 28 y, measured 15%
BMI 27.8
Est. ~23.6% vs measured 15%
BMI = weight (kg) ÷ height (m)²
Body fat % ≈ 1.20 × BMI + 0.23 × age − 10.8 × (male) − 5.4
Demo: 1.2×27 + 0.23×32 − 10.8 − 5.4 ≈ 23.6%
Category label: Overweight (25–29.9)
| BMI (kg/m²) | Category | Teaching note |
|---|---|---|
| < 18.5 | Underweight | May reflect low mass or illness—context matters |
| 18.5 – 24.9 | Normal weight | Screening band—not proof of healthy adiposity |
| 25 – 29.9 | Overweight | Often overlaps higher cardiometabolic risk |
| 30 – 34.9 | Obesity class I | Many guidelines intensify lifestyle/metabolic workup |
| 35 – 39.9 | Obesity class II | Higher weight-related comorbidity rates |
| ≥ 40 | Obesity class III | Severe obesity category in WHO framing |
| Sex | Athletic | Fitness | Average | Elevated |
|---|---|---|---|---|
| Men | < 14% | 14 – 17% | 18 – 24% | ≥ 25% |
| Women | < 22% | 22 – 24% | 25 – 31% | ≥ 32% |
| Method | What it measures | Strengths | Limitations |
|---|---|---|---|
| BMI (kg/m²) | Total mass vs height | Cheap, reproducible, global screening | Ignores muscle, bone, fat distribution |
| Deurenberg regression | Predicted % fat from BMI+age+sex | Quick population estimate | Biased in athletes; not ethnicity-calibrated |
| BIA scale | Impedance → % fat algorithm | Home tracking of trends | Hydration-sensitive; opaque formulas |
| Skinfolds | Subcutaneous fat thickness | Inexpensive field tool | Technician-dependent; equations vary |
| DEXA | X-ray tissue compartments | Research reference | Cost, radiation, access |
Discussed as “normal-weight obesity” in research—add waist, lipids, glucose
Example: BMI 24, estimated fat ~32% (female, older age)
Common in resistance-trained adults—BMI misclassifies lean mass as “excess weight”
Example: BMI 28, measured fat 15% on reliable testing
Often hydration, device, or visceral fat not captured by BMI alone
Example: Regression 23%, BIA scale 30% same week
BMI = 78 ÷ 1.70² ≈ 27 kg/m² → Overweight (25–29.9)
Estimated fat ≈ 23.6% (Average range (male))
Fat mass ≈ 18.4 kg, lean mass ≈ 59.6 kg
Higher BMI with lower estimated body fat% — can occur with resistance training and larger lean mass. Regression estimates are often biased in athletes; prefer direct body composition testing if decisions depend on it.
Education only. Not for diagnosing obesity, eating disorders, or prescribing diet/exercise. Athletes, pregnancy, edema, and ethnicity-specific norms need specialist interpretation.
For nutrition, sports medicine, and public health teaching
Suggested hashtags: #BMI #BodyFat #Anthropometry #Calculator