Free Body Fat Calculator (US Navy + BMI Methods)
Updated September 2026
Calculate body fat percentage using the US Navy method (tape measurements) or BMI-based estimate. Free, instant, no sign-up — metric and imperial supported.
Verified Capabilities
US Navy tape-measurement method and BMI-based (Deurenberg) method, each with their own inputs and accuracy notes.
Both methods use different coefficients for men and women, with an extra hip measurement for women in the Navy method.
Download your body fat percentage, category, and method as a CSV or plain-text file.
Fat mass and lean mass in kg/lbs are only shown for the BMI method — the Navy method never asks for body weight, so it can't compute mass breakdowns.
Body fat percentage measures how much of your total body weight is fat tissue, as opposed to lean mass — muscle, bone, water, and organs. Unlike BMI, which only divides weight by height squared, body fat percentage separates fat from muscle. This matters because a muscular athlete and a sedentary person can have identical BMI values but very different body compositions and health risks.
Body Fat Percentage Ranges by Gender
The American Council on Exercise (ACE) uses these classifications:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
How the US Navy Body Fat Formula Works
The US Navy method estimates body fat from simple tape measurements — no calipers, DEXA scan, or gym equipment required. For men, the formula uses height, neck, and waist circumference. For women, hip circumference is added because women carry proportionally more fat in that region.
Research shows the Navy method is accurate to within ±3–4 percentage points compared to DEXA scans for most people — reliable enough for tracking body composition changes over weeks and months.
US Navy Method vs BMI-Based Estimate
The BMI-based method (Deurenberg 1991 formula) estimates body fat from your BMI, age, and sex. It requires only weight and height but is less precise (±5%), particularly for muscular individuals where BMI overstates fatness. The Navy method is more accurate when you have a tape measure available. Use BMI-based as a quick estimate when tape measurements aren't practical.
How to Reduce Body Fat
- Calorie deficit: losing 0.5–1% of body weight per week requires roughly a 500–750 calorie daily deficit
- Resistance training: preserves lean muscle while in a deficit, improving your body fat ratio even when scale weight barely moves
- Protein intake: target 1.6–2.2 g per kg of body weight daily to protect muscle mass during fat loss
- Sleep: poor sleep raises cortisol, which promotes fat storage — especially visceral fat
- Consistency over intensity: body fat percentage changes slowly; track trends over 4–8 weeks, not day to day
How the Body Fat Calculator works
Select method: US Navy Method (tape measurements) or BMI-based estimation.
For Navy Method: enter height, neck circumference, and waist circumference (women also enter hip circumference).
For BMI Method: enter height, weight, and age — this method also reports fat mass and lean mass in lbs/kg, which the Navy method does not since it doesn't collect your body weight.
Click Calculate to see body fat percentage, fitness category, and a visual scale showing where your result falls.
Tips & tricks
- Only the BMI-based method reports fat mass and lean mass in kg/lbs — the Navy tape-measurement method shows body fat percentage and category only, since it never collects your body weight.
- For women, the hip measurement field only appears after selecting Female as the gender, since the Navy formula for women needs it.
- Switch between Metric and Imperial units at any time — labels and placeholders update, and previously entered values convert automatically.
Frequently Asked Questions
What is a healthy body fat percentage?
American College of Sports Medicine healthy ranges: Men: 10–22% (essential fat: 2–5%). Women: 20–32% (essential fat: 10–13%). Athletes: Men 6–13%, Women 14–20%. Obese: Men >25%, Women >32%.
How accurate is the US Navy body fat formula?
The Navy method is accurate within ±3–4% of DEXA scan measurements for most people. It's a reliable estimate for tracking trends over time. DEXA (dual-energy X-ray absorptiometry) is the gold standard but requires medical equipment.
Does the Navy method also show my fat mass and lean mass in kg/lbs?
No — only the BMI-based method shows fat mass and lean mass, because it collects your body weight as an input. The Navy method only outputs a body fat percentage, category, and method note, since it never asks for your weight.
What measurements do I need for the Navy method?
Men: neck and natural waist (narrowest point). Women: neck, natural waist, and hips (widest point). Measure to the nearest 0.5 cm or ¼ inch. Take three measurements at each site and use the average.
What is visceral fat vs subcutaneous fat?
Subcutaneous fat lies under the skin (what you can pinch). Visceral fat surrounds internal organs in the abdominal cavity — more metabolically active and associated with higher cardiovascular and metabolic disease risk. Waist circumference is a proxy for visceral fat.
Is my data safe when using the Body Fat Calculator?
Completely safe. The Body Fat Calculator processes everything locally in your browser. No input data, results, or usage information is ever transmitted to or stored on any server.
How accurate are the Body Fat Calculator calculations?
The Body Fat Calculator uses clinically validated formulas such as the Mifflin–St Jeor or Harris–Benedict equations where applicable. Results are population-based estimates and can differ from measured values by 10–20% for individuals with atypical body composition. See our <a href="/methodology/">Methodology page</a> for full formula sources and references. Consult a qualified healthcare professional before making medical or dietary decisions.
Which formula does the Body Fat Calculator use?
The Body Fat Calculator uses an established, peer-reviewed formula endorsed by leading health organisations such as the WHO, CDC, or NIH where applicable. The specific formula is chosen for its validated accuracy across diverse adult populations under normal conditions.
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