Estimate your body fat percentage using the US Navy tape measure method — or get a quick estimate from your BMI and age. Find out where you fall compared to healthy ranges for your age and sex.
Body fat percentage is the proportion of your total body weight that is fat tissue. It is a direct measure of body composition — what your body is actually made of — rather than a proxy calculation. A healthy body fat percentage indicates you have enough essential fat for hormonal function, organ protection and energy storage, without the excess that drives metabolic disease.
BMI (Body Mass Index), by contrast, is simply weight divided by height squared. It cannot distinguish between muscle and fat. A muscular athlete and a sedentary person with excess visceral fat can share the same BMI while differing by 15 or more percentage points in body fat. This is the fundamental limitation that makes body fat percentage a more meaningful health marker.
Approximately 30% of people with a healthy BMI (18.5–24.9) have body fat percentages in the obese range — a condition called 'normal weight obesity'. They carry the same metabolic risks as people classified overweight by BMI, but BMI alone will not identify them. Body composition measurement is the only way to detect it.
The US Navy formula was developed for military fitness assessment and is one of the most widely validated field methods for estimating body fat. It requires only a tape measure and uses body circumferences as a proxy for body density, which is then converted to body fat percentage.
For men: BF% = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
For women: BF% = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
Measurement technique matters significantly. Waist is measured at the narrowest point for men and at the navel for women. The neck is measured just below the larynx (Adam's apple), sloping slightly downward. Hip measurement (women only) is taken at the widest point. Consistent technique gives consistent tracking, even if absolute accuracy varies.
Studies comparing the Navy formula to DEXA scanning — the gold standard for body composition measurement — find an error margin of approximately ±3–4 percentage points. This is accurate enough to track trends over time and to identify clearly high body fat percentages, but not precise enough for clinical body composition assessment.
For tracking purposes, this accuracy is perfectly adequate. If your body fat drops from 28% to 23% over six months, a ±4% error doesn't change the conclusion — you've made meaningful progress. Where the Navy method is insufficient is for marginal differences or clinical assessment, where DEXA or hydrostatic weighing would be more appropriate.
Take measurements in the morning before eating. Use a flexible but non-stretching tape measure. Pull snug but not tight — you should be able to fit a finger underneath. Take three measurements at each site and average them. Consistency in technique matters more than absolute precision.
Healthy body fat ranges widen with age — this is intentional and reflects normal physiology. The central reason is sarcopenia: the age-related loss of skeletal muscle that begins around age 30 and accelerates after 60. As muscle mass declines, fat mass tends to increase even without changes in diet or exercise. Older adults naturally carry more fat as a percentage of body weight — and the healthy ranges account for this.
| Age group | Men (healthy range) | Women (healthy range) |
|---|---|---|
| 20–29 | 8–20% | 16–28% |
| 30–39 | 11–22% | 17–29% |
| 40–49 | 13–25% | 20–32% |
| 50–59 | 15–27% | 22–34% |
| 60+ | 16–28% | 24–36% |
Women naturally carry higher body fat than men at every age — this is biologically normal and related to reproductive function, hormonal differences and different fat distribution patterns. The lower end of women's healthy ranges (Athletic category) still represents approximately 14–20% body fat.
| Category | Men | Women | Metabolic implications |
|---|---|---|---|
| Essential fat | <6% | <14% | Required for organ function; below this risks hormonal disruption |
| Athletic | 6–13% | 14–20% | Associated with high fitness; competitive athletes often in this range |
| Fitness | 14–17% | 21–24% | Good body composition; low cardiovascular risk |
| Average | 18–24% | 25–31% | Normal population range; metabolic risk begins to increase at upper end |
| Obese | 25%+ | 32%+ | Elevated risk of type 2 diabetes, cardiovascular disease, metabolic syndrome |
Body fat is not created equal. Subcutaneous fat sits beneath the skin and is the fat you can pinch — it is relatively metabolically inactive and primarily a concern for excess weight. Visceral fat surrounds the internal organs deep in the abdominal cavity and is metabolically active, secreting inflammatory hormones and fatty acids directly into the portal circulation that feeds the liver.
Visceral fat is the fat type strongly associated with type 2 diabetes, cardiovascular disease, non-alcoholic fatty liver disease and certain cancers. People with the same total body fat percentage can have very different visceral fat levels — the apple versus pear body shape distinction reflects this. Waist circumference is a reasonable proxy: above 94cm (37in) for men and 80cm (31.5in) for women is associated with increased risk; above 102cm (40in) and 88cm (34.5in) respectively indicates substantially elevated risk.
The most important insight about fat loss is that body fat percentage is a ratio — it can improve either by losing fat or by gaining muscle. Resistance training achieves both: it directly builds muscle (lowering the fat fraction) while also burning calories and improving insulin sensitivity, which reduces fat storage. Studies consistently show that resistance training combined with a caloric deficit preserves significantly more muscle than cardio-only approaches.
Fat loss requires a sustained caloric deficit — consuming less energy than you expend. A deficit of 300–500 kcal per day produces approximately 0.3–0.5kg of fat loss per week while minimising muscle loss. Protein intake is critical during this process: consuming 1.6g per kg of bodyweight per day provides the amino acids needed for muscle protein synthesis, preventing the muscle catabolism that would otherwise accompany fat loss. For a 75kg person, this is 120g of protein daily.
Sustainable fat loss is 0.5–1% of bodyweight per week. Reducing body fat by 5 percentage points typically takes 3–6 months with consistent effort. Attempting faster rates of fat loss accelerates muscle loss, drives hunger hormones higher (leptin falls, ghrelin rises) and ultimately proves unsustainable. Slower, consistent progress with resistance training produces far better long-term body composition outcomes.
Resistance training 3–4 times per week + modest caloric deficit (300–500 kcal/day) + 1.6g protein per kg bodyweight = optimal fat loss with muscle preservation. This approach simultaneously reduces fat percentage and builds or maintains the muscle that keeps metabolism elevated long-term.
BMI reflects total body mass relative to height. Body fat percentage reveals body composition. The key differences in what each metric tells you:
A bodybuilder at 100kg, 180cm has a BMI of 30.9 — clinically 'obese'. Their body fat percentage may be 12% — clearly athletic. BMI would falsely classify them as obese. Conversely, someone at 70kg, 175cm has a BMI of 22.9 — normal. If 35% of that weight is fat, they are at elevated metabolic risk that BMI completely misses.
Body fat percentage also reveals changes during weight-stable body recomposition — where someone gains muscle and loses fat simultaneously, showing no change on the scales but meaningful improvement in health and body composition. This scenario, common in people starting resistance training, is invisible to BMI but visible in body fat percentage measurement.