Body Fat Calculator

Body-fat percentage is one of the most meaningful indicators of fitness and health. This calculator uses the U.S. Navy circumference method to estimate your body fat from neck, waist, and hip measurements, giving you a practical alternative to expensive lab tests.

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Why Body-Fat Percentage Matters

Unlike BMI, body-fat percentage distinguishes between fat tissue and lean tissue (muscle, bone, water, organs). Two people can weigh exactly the same yet have vastly different body-fat levels, leading to different health risk profiles. Tracking body-fat percentage helps you monitor meaningful changes in body composition, especially when you are simultaneously gaining muscle and losing fat.

Essential fat is the minimum amount your body needs for normal physiological function. For men this is roughly 2-5%, and for women 10-13%. Dropping below essential levels can impair hormonal balance, immune function, and organ protection.

The U.S. Navy Method

This calculator uses the circumference-based formula developed by the U.S. Navy:

  • Men: %BF = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76
  • Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

All measurements should be taken in centimeters or inches at the sites specified: neck at the narrowest point, waist at the navel, and hips at the widest point (women only).

Interpreting Your Results

CategoryMenWomen
Essential Fat2 – 5%10 – 13%
Athletes6 – 13%14 – 20%
Fitness14 – 17%21 – 24%
Average18 – 24%25 – 31%
Obese25%+32%+

Limitations

The Navy method is a convenient estimate but has a margin of error of roughly 3-4%. It may be less accurate for very lean or very obese individuals. For clinical precision, consider hydrostatic weighing, DEXA scanning, or air-displacement plethysmography. Always discuss significant body-composition changes with a qualified healthcare provider.

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Frequently Asked Questions

How accurate is the Navy body-fat method?
The Navy method correlates well with hydrostatic weighing and typically falls within 3-4% of DEXA results for most individuals. Accuracy improves when measurements are taken consistently at the same sites and times of day. For clinical-grade precision, lab methods are recommended.
What body-fat percentage is considered healthy?
For men, 14-17% is generally classified as the fitness range, while 21-24% is comparable for women. Athletes often sit lower, but going below essential fat levels (2-5% men, 10-13% women) can be harmful. The ideal range depends on your age, goals, and overall health.
Can I lower my body-fat percentage without losing weight?
Yes. By gaining muscle while losing fat, you can reduce your body-fat percentage even if the scale stays the same or goes up slightly. Resistance training combined with adequate protein intake is the most effective strategy for this kind of recomposition.
How often should I measure body fat?
Every 4-6 weeks is a reasonable frequency. Body-fat changes happen gradually, and measuring too often can be misleading due to hydration shifts and measurement variability. Consistency in measurement conditions matters more than frequency.
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