Body Fat Calculator
Estimate body fat percentage with the US Navy tape method, plus lean mass, fat mass, and where you sit against the standard fitness categories.
How to use this calculator
- 1Measure first thing in the morning, before eating, with the tape snug but not compressing the skin.
- 2Measure your neck just below the larynx, letting the tape slope slightly downward at the front.
- 3Measure your waist at the navel if you are male, or at the narrowest point if you are female.
- 4If you are female, also measure your hips at their widest point.
- 5Take each measurement three times and use the average.
How it works
US Navy body fat formula
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 Fat mass = weight × %BF Lean mass = weight − fat mass All circumferences in inches
The method works because fat is distributed in predictable places. Waist circumference tracks abdominal fat, while neck circumference is largely lean tissue, so the difference between them is a strong proxy for total fat. Height normalises for frame size. The logarithmic form was fitted against hydrostatic weighing on a large military population, which is why it is accurate on average but less so at the extremes.
Worked example
A man 70 inches tall weighing 180 lb with a 34-inch waist and a 15.5-inch neck: log₁₀(34 − 15.5) = 1.2672 and log₁₀(70) = 1.8451, giving about 16.5% body fat — roughly 29.7 lb of fat and 150.3 lb of lean mass, which sits in the fitness range.
Body Fat Calculator: the complete guide
Why body fat percentage beats BMI
BMI only knows your height and weight, so it cannot tell muscle from fat. A muscular athlete and a sedentary person of the same height and weight get the same BMI despite completely different body composition — which is exactly why the armed forces adopted a tape test as a secondary screen.
Body fat percentage answers the question BMI is really being used as a proxy for: how much of your mass is fat tissue. It also gives you lean body mass, which is the number that matters for protein targets, drug dosing, and tracking whether a diet is costing you muscle.
What the categories mean
Essential fat — around 3–5% for men and 10–13% for women — is the minimum needed for hormone production, nerve insulation, and organ protection. Below it, health consequences follow quickly, and for women menstrual function is usually the first thing to go.
The athletic and fitness bands describe people who train consistently. Average describes most of the adult population and is not itself a health problem. The obese band is where metabolic risk starts to rise sharply, particularly when the fat is carried around the abdomen rather than the hips and thighs.
Bands shift with age. Body fat naturally rises a few points per decade as lean mass declines, and a percentage that would be high at 25 is unremarkable at 55.
Measuring accurately
Tape technique is the largest source of error in this method — far larger than the formula itself. Use a flexible non-stretch tape, keep it horizontal and parallel to the floor, and pull it snug enough to sit against the skin without indenting it. Measure at the end of a normal exhale, never while holding your breath or sucking in.
Consistency matters more than absolute accuracy when tracking change. Measure at the same time of day, in the same conditions, and take three readings at each site to average. A single measurement's worth of noise can easily be a full percentage point of apparent body fat.
How this compares to other methods
DEXA scanning is the practical gold standard, accurate to about 1–2 percentage points and able to report where the fat sits. Hydrostatic weighing is similarly accurate but awkward. Both need a clinic appointment.
Bioelectrical impedance scales are convenient but highly sensitive to hydration — the same person can read three points apart morning and evening. Skinfold calipers are accurate in trained hands and unreliable otherwise. The Navy tape method sits in a useful middle ground: free, repeatable, and typically within about three points of DEXA.
Frequently asked questions
How accurate is the Navy body fat method?
Studies put it within about 3 percentage points of hydrostatic weighing for most people. It is least accurate at the extremes — very lean athletes tend to be overestimated, and people carrying a lot of abdominal fat tend to be underestimated. For tracking change over time it is more reliable than the absolute figure suggests.
What is a healthy body fat percentage?
For men, roughly 8–19% is considered healthy, with 6–13% typical of athletes. For women, roughly 21–32% is healthy, with 14–20% typical of athletes. Below the essential-fat threshold — about 3–5% for men and 10–13% for women — is not sustainable and carries real health risks.
Why does the female formula need a hip measurement?
Women store proportionally more fat around the hips and thighs, so waist circumference alone misses a large share of it. Adding hip circumference captures that distribution, which is why the female version of the formula is a three-site measurement rather than two.
How fast can I lower my body fat percentage?
A deficit of about 500 calories a day loses roughly one pound of fat per week, which is around half a percentage point of body fat per month for most people. Faster losses increasingly come from lean tissue. Keeping protein high and resistance training regularly is what preserves lean mass while the fat comes off.