Body Fat Percentage Calculator
Estimate your body fat percentage using the US Navy circumference method — no equipment needed.
What is body fat percentage?
Body fat percentage (BF%) is the proportion of your total body weight that is composed of fat tissue. It is widely considered a more meaningful health marker than body weight or BMI alone, because two people of the same height and weight can have drastically different body compositions — one lean and muscular, the other with high fat mass and low muscle mass.
Body fat serves essential physiological functions. It insulates organs, stores energy, produces hormones (including sex hormones and leptin), and supports brain function. Having too little fat — below "essential fat" levels — is as dangerous as having too much. The health risks associated with excess body fat include insulin resistance, type 2 diabetes, cardiovascular disease, sleep apnoea, and certain cancers.
The US Navy circumference method
Developed by Hodgdon and Beckett at the U.S. Naval Health Research Center in 1984, this method estimates body fat from body circumference measurements and height. It requires only a soft measuring tape and takes about two minutes. While less accurate than laboratory methods, it is validated, reproducible, and practical for self-monitoring over time.
Men (all in cm):
BF% = 86.01 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women (all in cm):
BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387The male formula uses waist and neck only. For men, abdominal circumference minus neck circumference is a reliable proxy for visceral fat — the metabolically active fat stored around the organs. The female formula adds hip circumference to account for the different fat distribution pattern in women.
How to measure correctly
Body fat percentage categories
| Category | Men | Women | Description |
|---|---|---|---|
| Essential fat | 2–5% | 10–13% | Minimum fat for organ protection and hormonal function. Athletes rarely go this low. |
| Athletic | 6–13% | 14–20% | Typical of competitive athletes. Visible muscle definition. |
| Fitness | 14–17% | 21–24% | Healthy, active individuals. Good muscle tone with some fat covering. |
| Average | 18–24% | 25–31% | Typical for sedentary adults. Health risk begins to rise toward the upper end. |
| Obese | ≥ 25% | ≥ 32% | Associated with significantly elevated risk of metabolic disease. |
Note: These categories are from the American Council on Exercise (ACE). Other organisations (WHO, ACSM) use slightly different cut-offs. Age also matters: a 55-year-old with 22% body fat may be at lower health risk than a 25-year-old with the same reading, because body fat naturally increases with age.
How the Navy method compares to other techniques
| Method | Accuracy (±%BF) | Cost | Accessibility | Best for |
|---|---|---|---|---|
| DEXA scan | ±1–2% | High (€100–250) | Medical clinic | Gold standard; body composition research |
| Hydrostatic weighing | ±1–3% | High | Laboratory | Research; elite athlete assessment |
| Air displacement (Bod Pod) | ±2–3% | High | University labs | Paediatric and clinical populations |
| Skinfold calipers | ±3–5% | Low | Gym / trainer | Regular monitoring by trained testers |
| Bioimpedance (BIA) | ±3–8% | Medium | Home scales, gym | Convenient; hydration-sensitive |
| US Navy method | ±3–4% | Free | Self-measurement | At-home tracking; no equipment needed |
| BMI | Poor (body comp.) | Free | Universal | Population screening only |
Why body fat matters more than BMI
BMI (body mass index) divides weight by height squared. It cannot distinguish between muscle and fat, making it misleading for muscular individuals and sometimes for older adults who have lost muscle mass while gaining fat (a condition called "sarcopenic obesity"). Two people with identical BMIs of 25 kg/m² can have body fat percentages ranging from 10% to 35%, depending on their body composition.
Body fat percentage, especially when combined with waist circumference, better predicts metabolic risk. Excess abdominal (visceral) fat — which the Navy method indirectly captures through waist circumference — is specifically associated with insulin resistance, elevated triglycerides, low HDL cholesterol, and cardiovascular disease, regardless of total body weight.
Practical strategies to reduce body fat
- Caloric deficit: A sustained deficit of 300–500 kcal/day leads to approximately 0.3–0.5 kg of fat loss per week without excessive muscle loss.
- Adequate protein: Consuming 1.6–2.2 g of protein per kg of body weight preserves lean muscle during a caloric deficit and increases satiety.
- Resistance training: Lifting weights two to four times per week builds and preserves muscle mass, increasing resting metabolic rate and improving body composition independently of fat loss.
- Cardiovascular exercise: Zone 2 cardio (60–70% max heart rate) is particularly effective at fat oxidation. Aim for 150–300 minutes per week.
- Sleep: Chronic sleep deprivation elevates cortisol and ghrelin (hunger hormone), increasing appetite and fat storage. Aim for 7–9 hours per night.
- Consistency over 8–12 weeks: Body composition changes are slow. Track measurements monthly rather than weekly to see meaningful trends.
Frequently asked questions
How accurate is the Navy method compared to DEXA?
Studies comparing the Navy method to DEXA scanning report a typical error of ±3–4 percentage points. It tends to overestimate body fat in lean, muscular individuals and underestimate it in those who carry fat more centrally. For tracking changes over time, however, it is reliable — even if the absolute number has some error, the trend is meaningful.
Why does the formula not use age?
The Navy formula uses only circumference measurements and height. Age is not included because the circumference measurements already indirectly capture the fat distribution patterns that correlate with age. However, age is useful for interpreting your result — what is average for a 50-year-old is considered above-average fat for a 25-year-old.
Can I have a high body fat percentage and still be healthy?
Metabolically healthy obesity exists but is controversial. Research suggests that even with normal metabolic markers, excess body fat (particularly visceral fat) confers long-term cardiovascular and cancer risk. However, cardiorespiratory fitness appears to be at least as important as body fat percentage — a "fat but fit" individual has better health outcomes than a lean, sedentary person.
How often should I re-measure?
Monthly is ideal for tracking meaningful change. More frequent measurements introduce noise due to hydration, time of day, and measurement variability. Take three consecutive measurements each time and use the average.
US Navy circumference method: Men: 86.01×log₁₀(waist−neck) − 70.041×log₁₀(height) + 36.76 Women: 163.205×log₁₀(waist+hip−neck) − 97.684×log₁₀(height) − 78.387 All measurements in centimeters.