Body Fat Calculator

How to Use the Body Fat Calculator

The Body Fat Calculator estimates your body fat percentage using the U.S. Navy circumference method. This approach requires only a few body measurements and provides a reasonably accurate estimate without expensive equipment like DEXA scans or hydrostatic weighing.

Taking Measurements

You will need a flexible measuring tape. For men, measure your waist at the navel and neck at the narrowest point below the Adam apple. For women, also measure your hips at the widest point. Enter your height as well. Take measurements in the morning before eating for consistency.

The Navy Method Formula

Men: Body Fat % = 86.010 × log10(waist - neck) - 70.041 × log10(height) + 36.76

Women: Body Fat % = 163.205 × log10(waist + hip - neck) - 97.684 × log10(height) - 78.387

These formulas use circumference measurements in inches and have been validated against hydrostatic weighing with good correlation.

Body Fat Categories

For men: Essential fat is 2-5%, Athletic is 6-13%, Fitness is 14-17%, Average is 18-24%, Obese is 25% and above. For women: Essential fat is 10-13%, Athletic is 14-20%, Fitness is 21-24%, Average is 25-31%, Obese is 32% and above. Women naturally carry higher essential fat for reproductive health.

Lean Body Mass

The calculator also shows your lean body mass (everything except fat: muscles, bones, organs, water). Lean Mass = Total Weight × (1 - Body Fat %). A 180 lb person at 20% body fat has 36 lbs of fat and 144 lbs of lean mass. Tracking lean mass is important during weight loss to ensure you are losing fat, not muscle.

Improving Body Composition

To reduce body fat, maintain a moderate calorie deficit while eating adequate protein (0.7-1g per pound of bodyweight) and performing resistance training. This approach preserves muscle mass while burning fat, improving your body composition even if the scale moves slowly.

Frequently Asked Questions

Q: How accurate is the Navy method?

A: The Navy method is typically accurate within 3-4% of DEXA scan results. It is more accurate than BMI for assessing body composition but less precise than laboratory methods. Consistent measurement technique improves reliability for tracking changes over time.

Q: How often should I measure body fat?

A: Measure every 2-4 weeks. Body composition changes slowly, and daily fluctuations in hydration and food intake can affect measurements. Take measurements at the same time of day under the same conditions for meaningful comparisons.

Q: Can I have too little body fat?

A: Yes. Essential body fat is necessary for organ protection, hormone production, and temperature regulation. Men below 3-5% and women below 10-13% body fat may experience hormonal disruption, weakened immunity, and other health issues. Extremely low body fat is not sustainable or healthy long-term.