A scale tells you weight. Body fat percentage tells you what kind of weight. This calculator uses the U.S. Navy Method, three simple measurements with a soft tape, to estimate body fat % within 3% of a DEXA scan, free, with no calipers required.
The U.S. Navy Method estimates body fat using waist, neck, and height (plus hip for women), typically within ±3% of DEXA. Healthy lean ranges: men 10-17%, women 18-25%. Athletic men sit 6-13%; athletic women 14-20%. Body fat below 5% (men) or 12% (women) is competition territory and not sustainable. Pairs with BMI and ideal body weight to give a complete picture.
Source: Hodgdon JA, Beckett MB. Naval Health Research Center 1984↑ These are example numbers. Calculate above to replace them with yours.
A 22-year-old at 12% BF and a 55-year-old at 12% BF are not the same picture. Body fat naturally rises with age, and what's "optimal" shifts with it. Below are the standardized ranges from ACE and ACSM.
| Age | Athletic | Fitness | Average | Above average |
|---|---|---|---|---|
| 20-29 | 6-13% | 14-17% | 18-24% | 25%+ |
| 30-39 | 7-14% | 15-18% | 19-24% | 25%+ |
| 40-49 | 8-15% | 16-20% | 21-25% | 26%+ |
| 50-59 | 9-17% | 18-21% | 22-26% | 27%+ |
| 60+ | 10-18% | 19-22% | 23-27% | 28%+ |
Essential fat (men): 2-5% • Essential fat (women): 10-13%. Below essential = clinically dangerous.
Body fat is one signal. Whether any protocol is appropriate for you is decided by a U.S.-licensed physician after reviewing your history, labs, and goals, not by a calculator.
Take the 60-second quiz. A U.S.-licensed physician reviews your information and builds a plan around your goals. Membership includes the consultation, ongoing medical care, and a muscle-preservation guide when a weight-loss medication is prescribed.
Find my protocol Test then treatCircumference math is an estimate. A comprehensive lab panel, testosterone, free T, SHBG, fasting glucose, HbA1c, lipids, thyroid, cortisol, and inflammatory markers, shows what's actually driving your numbers so any plan starts from data.
See lab panelsBody fat % is one number. These four tools fill in the rest of the system, calories, protein, hormones, and aging.
Hand-picked guides from our research library covering the science of fat loss, and hormonal levers.
Garbage in, garbage out. Use a soft, flexible tape (a cloth or fiberglass tape works, not metal). Measure on bare skin, first thing in the morning if possible, and pull the tape snug but not compressed against the skin.
The U.S. Navy method (Hodgdon & Beckett, 1984) uses log-transformed circumference ratios:
Men: BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
All measurements in inches. Validation studies against hydrostatic weighing show ~3-4% mean error, comparable to skinfold calipers in untrained hands and only slightly worse than DEXA in non-extreme physiques.
It depends on what you're optimizing for:
Body fat % is dramatically more useful than BMI for individuals. BMI cannot distinguish a 200-lb lifter at 12% BF (athletic) from a 200-lb sedentary man at 32% BF (obese), the BMI is identical. Body fat %, by contrast, captures the actual signal: how much of your weight is fat vs. lean mass.
The exception: BMI is fine for population-level epidemiology and rough screening. For your personal target, body fat % beats it. Use our BMI calculator for the quick screen and this tool for the real target.
For non-extreme physiques (BMI 18-35), the Navy method tracks within ~3% of DEXA scans on average. It loses accuracy in two cases: very lean physiques (skews high) and very obese physiques (skews low). For everyone in between, it's the most accurate at-home method without specialized equipment.
Every 2-4 weeks if actively cutting or bulking. Body fat doesn't change in days, give it time. More frequent measurement causes you to chase noise. Same conditions every time: morning, fasted, after the bathroom, before training.
It usually doesn't actually, but circumferences can shift in confusing ways early in lifting. Your waist may temporarily increase from spinal-erector and oblique growth. Your neck may grow from traps and SCM. Trust trends over 8+ weeks, not week-to-week noise.
If you're a man over 30 and 5+ points above the optimal range, the order of operations is usually: (1) get a comprehensive lab panel including testosterone, SHBG, glucose, HbA1c, and lipids, (2) calculate maintenance calories with our TDEE calculator and protein target with our protein calculator, (3) review your options with a U.S.-licensed physician who decides what, if anything, is appropriate based on your labs, (4) start a structured lifting program 3-4 days per week. The single biggest mistake is trying willpower alone when the underlying physiology is broken.
Below 5% (men) or 14% (women) chronically is dangerous, it disrupts testosterone, immune function, sleep, and bone density. If you're a competitive athlete it may be temporarily appropriate; for everyone else, it's a sign to eat more and train smarter, not less.
During any period of fat loss, adequate protein intake (commonly cited at ~0.7-1.0 g per lb of goal body weight) and resistance training are the two most consistently studied levers for protecting muscle while losing fat (Helms et al., J Int Soc Sports Nutr, 2014; Stiegler & Cunliffe, Sports Med, 2006). Whether any protocol is appropriate for you is decided by a U.S.-licensed physician after reviewing your history, labs, and goals.
This calculator uses the U.S. Navy circumference method, a validated field estimate of body fat. Tape methods are estimates and less precise than a DEXA scan. It is for education only and is not medical advice.
How this tool calculates
Body fat percentage is estimated using the Hodgdon-Beckett U.S. Navy circumference method, which uses waist, neck, and height (plus hip for women). Validation studies show accuracy within approximately ±3% body fat compared to DEXA in non-extreme physiques. Less accurate for elite athletes or BMI >40.
Peer-reviewed sources
Important. This tool is provided for educational purposes only and does not constitute medical advice, diagnosis, or treatment. The tool does not prescribe medication, recommend specific dosing, or substitute for clinical evaluation. Compounded medications referenced anywhere on this site are not FDA-approved; the FDA does not verify the safety, effectiveness, or quality of compounded drugs. Treatment decisions are made only by a licensed U.S. physician after individual patient evaluation.
OPTML offers compounded semaglutide and tirzepatide, prescribed and overseen by U.S.-licensed physicians. Compounded drug products are not approved or evaluated for safety, effectiveness, or quality by the FDA. OPTML is not associated with, endorsed by, or affiliated with the manufacturers of FDA-approved branded weight-loss medications, and does not sell or supply those branded products. Anyone interested in an FDA-approved branded medication should consult a licensed healthcare provider or pharmacist. Individual results vary; no specific result is promised, and weight management requires ongoing medical guidance.
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