Body Fat Calculator
BMI‑based method · age & gender adjusted · fast estimate
📘 Based on Deurenberg formula (BMI + age + gender). Valid for adults 18–100 years.
Estimated body fat
— %
—
Fat Mass — kg / lb
Lean Body Mass — kg / lb
Healthy range (age‑adjusted) — %
| Category | Women | Men | Essential fat | 10–13% | 2–5% | Athletes | 14–20% | 6–13% | Fitness | 21–24% | 14–17% | Average | 25–31% | 18–24% | Obese | 32+% | 25+% |
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⚕️ Clinical estimate — not a substitute for professional assessment.
What a Body Fat Calculator Actually Does
- It estimates, not measures – A body fat calculator uses formulas (e.g., US Navy method, BMI-based estimation) to predict body fat percentage. It’s not as accurate as DEXA scans or hydrostatic weighing, but it’s free and instant.
- Body fat percentage ≠ BMI – BMI only uses height and weight. Body fat calculators use additional inputs like neck, waist, and hip circumference (US Navy method) or age and gender. Two people with the same BMI can have very different body fat percentages.
- The US Navy method is the most common – Developed by the Naval Health Research Center, this method uses neck, waist, and (for women) hip circumferences. It has a margin of error of about 3–4% compared to laboratory methods.
Best Practices for Users
- Measure at the same time daily – Body fat circumference measurements can fluctuate by 1–2% throughout the day. Best practice: measure upon waking, before eating or drinking, after using the bathroom.
- Track trends, not single readings – A single body fat calculation might be off. Monthly averages over 3–6 months show true progress. Weekly measurements are too frequent for meaningful trends.
- Don’t obsess over the number – A body fat percentage of 18% vs 19% is meaningless due to measurement error. Focus on the healthy range (e.g., 10–20% for young men, 18–28% for young women).
- Combine with other metrics for best insight – Use body fat calculator alongside: waist circumference, how clothes fit, energy levels, blood pressure, and strength measurements.