Body Fat Calculator
Estimate your body fat percentage using the U.S. Navy tape method. Enter a few measurements in inches to get your body fat and fitness category.
Measure at the widest point for waist/hip and just below the larynx for neck, in inches. The U.S. Navy tape method is an estimate (±3–4%); calipers or a DEXA scan are more precise. Not medical advice.
How to use this calculator
Select your biological sex, then enter your height, neck, and waist measurements in inches. Women also enter their hip measurement. Click Calculate and the tool returns your estimated body fat percentage and the fitness category it falls into. No equipment beyond a soft measuring tape is required.
How the U.S. Navy method works
The U.S. Navy circumference method was developed to give military personnel a practical, field-ready alternative to underwater weighing. The insight behind it is straightforward: fat tends to accumulate around the waist (and hips in women) more than around the neck. By comparing the circumference of fat-storage areas to leaner areas (neck) and factoring in height, the formula can estimate what proportion of body mass is fat.
The calculation uses natural logarithms of the measurements rather than the raw numbers, which improves accuracy across a wide range of body sizes. The formula was originally validated against hydrostatic (underwater) weighing, which was the gold-standard body composition method at the time of development.
How to take accurate measurements
Small measurement errors have an outsized effect on the result, so technique matters. Follow these guidelines for the most consistent readings:
- Neck: Measure just below the larynx (Adam's apple), with the tape perpendicular to the long axis of the neck. Do not flex your neck downward — stand tall and look straight ahead.
- Waist (men): Measure at the level of the navel. Breathe out naturally and take the measurement at the end of the exhale — do not suck in.
- Waist (women): Measure at the narrowest point of the torso, typically 1–2 inches above the navel.
- Hips (women): Measure at the widest point of the hips and buttocks, with feet together.
Use a flexible tape measure, keep it parallel to the floor, and hold it snug against the skin without compressing the tissue. Take each measurement twice and average the two readings. Measure on bare skin whenever possible, and at the same time of day — morning before eating is ideal for tracking over time.
Worked example — step by step
A man who is 70 inches tall with a 15.5-inch neck and a 34-inch waist:
- log₁₀(34 − 15.5) = log₁₀(18.5) ≈ 1.267
- log₁₀(70) ≈ 1.845
- Body fat % = 86.010 × 1.267 − 70.041 × 1.845 + 36.76 ≈ 15.6%
That result falls in the "fit" category for men (roughly 14–17%). A one-inch error in the waist measurement can shift the result by about 2–3 percentage points, which underscores why consistent technique matters more than the exact formula.
How to interpret your result
Body fat percentage is more informative than weight alone because it tells you what your weight is made of. Two people can weigh the same but have very different body compositions. As a general guide:
- Men: Essential fat ≈ 2–5% · Athletic ≈ 6–13% · Fit ≈ 14–17% · Average ≈ 18–24% · Overfat ≈ 25%+
- Women: Essential fat ≈ 10–13% · Athletic ≈ 14–20% · Fit ≈ 21–24% · Average ≈ 25–31% · Overfat ≈ 32%+
Essential fat is the minimum required for normal organ function and hormone production. Going below essential fat levels is dangerous. If your result is in the overfat range, speak with a healthcare provider about next steps — body fat percentage alone does not determine health risk.
Common mistakes to avoid
- Measuring over clothing. Even thin fabric adds measurement inches and skews the result upward.
- Holding your breath or flexing while measuring the waist. Waist circumference should be taken at the end of a normal exhale, relaxed.
- Taking only one measurement. Taking the average of two readings reduces the impact of tape placement variation.
- Measuring at different times of day. Body circumferences fluctuate with food intake and hydration. Measure at the same time — ideally morning — for comparable tracking data.
The formula
Men: %fat = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women: %fat = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
Results are estimates. Body fat percentage is not a medical diagnosis. Consult a healthcare professional for individualized guidance on body composition goals.
How we calculate this
Body fat percentage is estimated using the U.S. Navy circumference method, which applies a logarithmic formula to height, neck, waist, and (for women) hip measurements. The equation was developed and validated by the U.S. Navy against hydrostatic weighing data. Results are estimates; individual accuracy varies.
Sources
Frequently asked questions
How does the U.S. Navy body fat method work?
It estimates body fat percentage from circumference measurements taken with a tape measure. For men, the formula uses height, neck circumference, and waist circumference. For women it also includes hip circumference. Those values are plugged into a logarithmic equation that was validated against hydrostatic weighing data by the U.S. Navy.
How accurate is the Navy body fat method?
The Navy method is typically within 3–4 percentage points of laboratory methods such as DEXA scans or hydrostatic weighing for most people. It tends to be slightly less accurate for individuals at the extremes of body fat — very lean or very high body fat. Accuracy depends heavily on consistent and correct measurement technique.
Where exactly do I take each measurement?
Measure your neck just below the larynx (Adam's apple), keeping the tape perpendicular. Measure your waist at the navel for men, or at the narrowest point of the torso for women. Women measure hips at the widest point of the buttocks. Keep the tape snug against the skin — not compressed — and parallel to the floor.
What is a healthy body fat percentage?
General reference ranges: men at 6–13% are considered athletic, 14–17% fit, 18–24% average, and 25% or above overfat. Women at 14–20% are athletic, 21–24% fit, 25–31% average, and 32% or above overfat. Essential fat — the minimum needed for basic physiological function — is about 2–5% for men and 10–13% for women.
How does body fat percentage differ from BMI?
BMI uses only height and weight and cannot distinguish fat from muscle. Body fat percentage directly estimates how much of your mass is fat tissue versus lean tissue. Two people can share the same BMI but have very different body fat levels, which is why body fat percentage is often a more meaningful measure of body composition.
How often should I re-measure?
Monthly re-measurement is a reasonable frequency for tracking changes. Day-to-day fluctuations from hydration, food volume, and measurement angle can create noise, so measuring at the same time of day (morning, before eating) under the same conditions improves consistency.
Is body fat percentage a more reliable health marker than BMI?
For most purposes, yes. Body fat percentage tells you how much of your body is actually fat tissue, which is more directly related to metabolic health risk than the BMI ratio. However, no single number tells the whole story — where fat is distributed, particularly visceral fat around the organs, also matters greatly.