Body Fat Calculator: U.S. Navy Method for Body Fat Percentage, Fat Mass and Lean Body Mass
Free online body fat percentage, fat mass and lean body mass (LBM) calculator using the U.S. Navy circumference method. Enter your sex, height, weight and neck, waist (and hip for women) measurements in metric or imperial units to get a gender-specific body-fat category, fat mass and lean mass. Results update live and can be saved to local history, with everything computed privately in your browser.
Body circumferences
U.S. Navy circumference method
Body fat & lean mass
Body fat percentage, fat mass and LBM
The U.S. Navy method estimates body fat from height, neck and waist (plus hip for women) using log-based formulas. It needs no calipers or DEXA, but can differ from a scale by about ±3%, which is normal.
How to Use
Body Fat & Lean Body Mass (LBM) Guide
U.S. Navy circumference method
Body fat percentage is the share of your total weight made up of fat and reflects body composition better than BMI. Lean Body Mass (LBM) = weight − fat mass and includes muscle, bone, organs and water. FinCompute uses the U.S. Navy circumference method, which estimates body fat from height, neck and waist (plus hips for women) using log formulas. No body-fat scale, calipers or DEXA required — just a tape measure at home — making it well suited to tracking trends over time.
01 Measuring circumferences correctly
Neck: measure just below the larynx at the narrowest point, looking straight ahead without tilting the chin down. Waist: at the narrowest point between the lowest rib and the iliac crest, at the end of a normal breath — do not suck in. Hips: around the widest part of the buttocks, keeping the tape level and snug without compressing the skin.
Men: BF% = 495 ÷ (1.0324 − 0.19077·log10(waist−neck) + 0.15456·log10(height)) − 450. Women: BF% = 495 ÷ (1.29579 − 0.35004·log10(waist+hip−neck) + 0.22100·log10(height)) − 450. All circumferences are in centimeters.
- Measure in the morning, fasted, in light clothing
- Keep the tape horizontal and against the skin without compressing tissue
- Take 2–3 readings and average them to reduce error
- The circumference method is less precise than DEXA for "apple" vs. "pear" shapes
02 Healthy body fat ranges
American Council on Exercise (ACE) reference ranges for adults: men — essential 2–5%, athletes 6–13%, fitness 14–17%, acceptable 18–24%, obese ≥25%; women — essential 10–13%, athletes 14–20%, fitness 21–24%, acceptable 25–31%, obese ≥32%. Women need higher essential fat for reproduction.
Lean mass is the main driver of basal metabolism. Building LBM through resistance training raises your resting burn even if your scale weight does not change. During fat loss, protect LBM with strength training and enough protein.
Inputs
- Metric / ImperialSwitches between cm/kg and in/lb input fields.
- sexSelects the Navy-circumference formula (hips are required for women).
- heightYour height.
- neckNeck circumference at the narrowest point.
- waistWaist circumference at the narrowest point.
- hipsHip circumference (women only).
Actions
- CalculateBody-fat % and lean mass update live as you type; this button saves the result to the history drawer.
- ResetRestores the default inputs.
- Circumference, scale and caliper results can differ by ±3–5%; stick to one method for trends
- A shrinking waist with stable weight usually means fat lost and muscle gained — a positive sign
- Long-term body fat above 25% (men) / 32% (women) raises metabolic syndrome risk
- Chasing very low body fat (men <6%, women <14%) can disrupt hormones and immunity
- Measure every 2–4 weeks at the same time with the same tool to avoid daily noise
Body fat percentage is the share of your total weight made up of fat and reflects body composition better than weight or BMI. This calculator uses the U.S. Navy circumference method — just a tape measure for height, neck, waist (and hips for women) — to estimate body fat percentage, fat mass and lean body mass (LBM), with centimeter or inch units, ideal for self-measurement at home.
The U.S. Navy circumference method
The men’s formula uses height, neck and waist; the women’s formula adds hip circumference, both via log-based equations. Developed by the U.S. Navy in the 1980s for body-fat screening, it needs no calipers or scale. Its downside is lower precision than DEXA or Bod Pod — expect around ±3% difference from a body-fat scale.
How to measure correctly
Measure the neck just below the larynx and above the collarbones, the waist at the narrowest point above the navel (natural waist) without sucking in, and the hips at the widest part. Keep the tape level and snug without compressing the skin, and measure at a normal exhale. Use the same unit (all cm or all inches) for every measurement.
Body fat categories (ACE reference)
Per the American Council on Exercise: women — essential fat 10–13%, athletes 14–20%, fitness 21–24%, average/acceptable 25–31%, obese ≥32%; men — essential 2–5%, athletes 6–13%, fitness 14–17%, average/acceptable 18–24%, obese ≥25%. Women need significantly more essential fat for physiological reasons.
Lean body mass and fat mass
Fat mass = weight × body fat percentage; lean body mass (LBM) = weight − fat mass, covering muscle, bone, organs and water. LBM is the main driver of resting metabolism, so building it through resistance training raises how many calories you burn at rest. Aim to preserve LBM while losing fat mass.
FAQ
QHow do I measure for the Navy body fat formula?
Men need height, neck and waist; women add hip. Measure the neck below the larynx, the waist at its narrowest point above the navel, and hips at the widest part, with the tape level and snug, all in the same unit.
QWhat is a healthy body fat percentage?
ACE references: men 14–17% fitness and 18–24% acceptable; women 21–24% fitness and 25–31% acceptable. Women carry more essential fat than men.
QIs the Navy method accurate?
It is a simple screening tool less precise than DEXA or Bod Pod, with roughly ±3% variation from scales. Measurement technique matters a lot — measure under the same conditions over time to track trends.
QWhat is lean body mass (LBM)?
LBM = weight − fat mass and includes muscle, bone, organs and water. It drives most of your resting metabolism, so increasing LBM helps sustain a healthy weight long term.
QWhat is the most accurate way to measure body fat at home?
Beyond circumference, options include bioelectrical-impedance scales (affected by hydration) and skinfold calipers (need practice). DEXA is the gold standard but costly. Pick one method and track trends under consistent conditions.