M ToolsMio

Body Fat Calculator

Estimate your body fat percentage with the US Navy tape method or from BMI. See your category, fat mass, and lean mass - free and 100% private.

Enter your measurements to see your body fat percentage.

Features

100% Browser-Based

Your measurements are never sent anywhere. Every calculation happens locally in your browser.

Free & No Sign Up

No registration, no limits, no hidden fees. Just open and use.

Instant Results

Your body fat percentage updates live as you type - no Calculate button, no waiting.

Two Proven Methods

Use the US Navy circumference formula with a tape measure, or the Deurenberg equation from your BMI - both in metric and US units.

More Than a Percentage

See your category on a visual scale, plus your body fat mass and lean body mass in kilograms or pounds.

How to Calculate Your Body Fat Percentage?

  1. Pick the Tape Measure (US Navy) method, or From BMI if you have no tape at hand.
  2. Choose Metric (cm, kg) or US (ft, in, lb) units - your values convert when you switch.
  3. Enter your sex, height, weight, and neck, waist, and hip measurements - results update live as you type.
  4. Read your body fat percentage, category, fat mass, and lean body mass.

Common Use Cases

Fitness Tracking

Body fat percentage is a better progress metric than weight - it tells you whether lost kilos are fat or muscle while cutting.

Bulking & Cutting Cycles

Know when to end a bulk or a cut: track your percentage against your target range instead of guessing from the mirror.

Military & Service Fitness

The US Navy circumference method is the actual tape test many services use - rehearse it before your assessment.

Health Screening

Body fat adds context BMI cannot give: two people with the same BMI can carry very different amounts of fat.

Tips for Accurate Results

Frequently Asked Questions

Is my data sent to any server?
No. The body fat calculator runs entirely in your browser using client-side JavaScript - your measurements and results are never transmitted, stored, or logged anywhere outside your device. Body measurements are sensitive personal information, which is exactly why this tool has no server-side component at all. You can verify it yourself: open your browser's DevTools Network tab, enter your values, and watch - zero requests leave your device.
How does the US Navy body fat formula work?
The US Navy method (developed by Hodgdon and Beckett in 1984) estimates body fat from body circumferences. For men it uses height, neck, and waist; for women it uses height, neck, waist, and hip. The measurements are combined in a logarithmic equation that correlates strongly with hydrostatic weighing. Published versions exist for both centimeters and inches; this tool converts your measurements to centimeters and applies the metric formula, so your result stays identical whichever unit system you type in.
How accurate is a body fat calculator?
The Navy circumference method typically has an error margin of about ±3-4% compared to laboratory methods like DEXA or hydrostatic weighing. It is most reliable for average-built people and less accurate for very muscular or very lean individuals. The BMI-based Deurenberg equation is a rougher estimate (±5% or more) because it cannot see body composition at all - it only knows your weight relative to your height. Use the tape method when you can, and treat any result as a trend indicator rather than an exact measurement.
What is a healthy body fat percentage?
For men, the American Council on Exercise classifies 6-24% as the healthy span: 6-13% for athletes, 14-17% for fitness, and 18-24% as average. For women, who physiologically carry more essential fat, the healthy span is 14-31%: 14-20% for athletes, 21-24% for fitness, and 25-31% as average. Below those ranges is essential fat (needed for basic physiology) and above them is classified as obese. Age shifts expectations slightly - a healthy range at 60 is a few points higher than at 25.
How do I measure my neck, waist, and hip correctly?
Use a flexible tape measure against bare skin, and take each measurement twice - if the two readings differ, take a third and use the median. Neck: measure just below the larynx (Adam's apple) with shoulders relaxed. Waist: men measure at the navel, women at the narrowest point of the abdomen, both after a normal exhale - do not pull the tape tight or suck in. Hip: measure around the widest part of the buttocks. Measure in the morning before eating for the most consistent day-to-day trend.

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