Estimate your body fat percentage with the U.S. Navy circumference method and compare it with a secondary BMI-based estimate. See estimated fat mass, lean body mass, BMI, and a general reference category.
This calculator provides an estimate for adults and is not a medical diagnosis or a substitute for professional body-composition testing.
Calculator
Use a flexible measuring tape and enter measurements without pulling the tape too tight.
Body Composition
Body fat percentage is the estimated proportion of total body weight that comes from fat mass. For example, a person who weighs 80 kg and has an estimated body fat percentage of 20% would have about 16 kg of fat mass under that estimate.
The rest of body weight is often described as lean body mass. Lean mass includes muscle, bone, organs, body water, connective tissue, and other non-fat components. Lean body mass is therefore not the same thing as skeletal muscle mass.
Body fat is a normal and necessary part of the human body. It stores energy, provides insulation, cushions tissues, and plays roles in normal physiological function. The amount and distribution of body fat vary with age, sex, genetics, training status, hormones, nutrition, and other factors.
Circumference Method
The method uses simple tape measurements and height to estimate body density and body fat percentage.
The metric form uses height, waist, and neck measurements in centimeters.
The female equation also uses hip circumference because the body-shape model includes an additional circumference measurement.
Small changes in circumference can change the result because the equations use logarithmic relationships between height and circumferences. For repeatable tracking, use the same tape, measurement locations, posture, and general conditions each time.
Measurement Guide
Stand upright without shoes. Keep your head level and use a wall or reliable height measurement if possible.
Measure around the neck just below the larynx. Keep the tape snug without compressing the skin.
For men, measure around the abdomen at the navel. For women, use the natural waist or the narrowest point according to the selected protocol.
For women, measure around the widest horizontal part of the hips and buttocks with the tape level.
Take measurements while relaxed rather than flexing or pulling in the abdomen. If you are tracking changes over time, measuring at a similar time of day and under similar conditions can make repeated estimates more comparable.
Secondary Estimate
A BMI-based body fat equation can provide a second estimate when age, height, weight, and sex are known. It does not use circumference measurements.
For adults, this calculator uses a common equation in which estimated body fat is derived from BMI and age, with different constants for males and females.
BMI cannot distinguish muscle from fat, so a BMI-based body fat estimate can be less useful for people with unusually high muscularity, unusual body proportions, or body composition that differs substantially from the population used to build the equation.
Reference Ranges
The ranges below are broad descriptive categories often used in fitness references. They are not individualized treatment goals and should not be interpreted as a diagnosis.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Higher range | 25%+ | 32%+ |
Once body fat percentage is estimated, the calculator can estimate fat mass by multiplying body weight by the body fat fraction. If someone weighs 80 kg at an estimated 20% body fat, estimated fat mass is 16 kg.
Lean body mass is then calculated by subtracting estimated fat mass from total body weight. In the same example, estimated lean mass would be 64 kg.
These values should be interpreted together with the uncertainty of the original body fat estimate. If the percentage estimate is off by several percentage points, the calculated fat mass and lean mass will also shift.
Lean mass is not a direct measurement of muscle. It includes all non-fat tissue and body water. A dedicated body-composition assessment may provide more detailed estimates of skeletal muscle, bone mineral content, visceral fat, or regional body composition.
Every body fat method has assumptions and sources of error. A circumference formula estimates body composition from external dimensions. A BMI equation estimates body fat from height, weight, age, and sex. Skinfold calipers estimate subcutaneous fat thickness. Bioelectrical impedance estimates body composition from electrical properties that can change with hydration.
More advanced methods such as DEXA, air-displacement plethysmography, and hydrostatic weighing use different physical measurements and models. Even those approaches can produce somewhat different results because body composition is not measured in exactly the same way by every technology.
For personal tracking, consistency can matter more than chasing a single exact number. If you use the Navy method, repeat the same measurement technique and compare trends over time rather than treating small day-to-day changes as precise changes in body fat.
If accurate body composition is important for medical care, athletic performance, research, or another high-stakes decision, use an appropriate professional assessment instead of relying on an online estimate alone.
A body fat percentage estimate is most useful when you understand what it can and cannot tell you. One calculation gives a snapshot based on the measurements entered at that moment. It does not measure where fat is stored, how much skeletal muscle you have, how strong or fit you are, or whether a particular percentage is appropriate for your medical situation.
If you are tracking changes over time, focus on the trend rather than a tiny movement in a single result. Tape placement, posture, breathing, hydration, recent meals, and ordinary measurement error can all change circumference values slightly. Repeating the same method under similar conditions usually makes comparisons more meaningful.
It can also be helpful to compare the Navy estimate with the BMI-based estimate shown by the calculator. A noticeable difference does not automatically mean one answer is wrong. The methods model body composition differently. Circumference equations respond to body shape, while BMI-based equations rely on height, weight, age, and sex.
Avoid treating a reference category as a required personal target. Broad body fat ranges are population reference tools, not personalized prescriptions. Age, training background, medical history, hormonal status, athletic goals, and other factors can affect how a body-composition result should be interpreted.
If you need a more precise assessment, consider a professionally administered method such as DEXA, air-displacement plethysmography, hydrostatic weighing, or another validated body-composition test. The right method depends on why you need the measurement, the level of accuracy required, cost, availability, and guidance from an appropriate health or fitness professional.
Important Limitations
The calculator converts measurements into an estimate using population equations. It cannot evaluate your overall health, nutritional status, fitness, or medical risk.
Frequently Asked Questions
The method combines height with circumference measurements. Men use waist and neck, while women use waist, hips, and neck.
No. It is an estimate based on circumference measurements and population equations. Tape placement, body shape, and measurement error can all affect the result.
Adults need age, weight, height, neck circumference, and waist circumference. The female Navy equation also requires hip circumference.
Lean body mass is total body weight minus estimated fat mass. It includes muscle, bone, organs, body water, and other non-fat tissue.
The two methods use different inputs and assumptions. The Navy method uses circumferences, while the BMI estimate uses height, weight, age, and sex, so different results are normal.
You can use repeated estimates as one tracking method, but keep your measurement technique consistent and avoid treating small changes as precise changes in body fat.