Body Fat Calculator
Estimate your body fat percentage using the US Navy circumference method
Your Results
Understanding Body Fat Percentage
Body fat percentage is the proportion of your total body weight that is composed of fat tissue. Unlike BMI, which only considers height and weight, body fat percentage provides a much clearer picture of your body composition by distinguishing between fat mass and lean mass (muscle, bone, water, and organs). Two people can have the same BMI but vastly different body fat levels, making this metric far more useful for assessing fitness and health risks.
The US Navy circumference method estimates body fat using simple tape measurements of your neck, waist, and (for women) hip circumferences along with your height. Developed for military fitness assessments, this method correlates well with more expensive techniques like DEXA scans and hydrostatic weighing, typically falling within 3-4% of clinical results. The formula uses logarithmic equations that account for the relationship between circumference sites and subcutaneous fat distribution.
Body fat serves essential biological functions, including insulation, organ protection, hormone production, and energy storage. Essential fat, the minimum amount needed for physiological function, is approximately 2-5% for men and 10-13% for women. Women naturally carry more body fat due to reproductive biology. Dropping below essential fat levels is dangerous and can lead to hormonal disruption, bone loss, and immune system compromise. For most people, a healthy range of body fat supports both optimal performance and long-term disease prevention.
To improve your body composition, focus on a combination of resistance training to build or maintain lean muscle mass and a moderate calorie deficit to reduce excess fat. Crash diets often lead to muscle loss, which raises your body fat percentage even as you lose weight on the scale. Track your measurements over time rather than relying on a single reading, as hydration, meal timing, and measurement technique can all cause day-to-day fluctuations of 1-2 percentage points.
How to Measure and Use This Calculator
- Select your gender using the toggle at the top of the form. This is important because the US Navy formula differs for men and women, and women require an additional hip measurement.
- Measure your neck circumference by wrapping a tape measure around your neck just below the larynx (Adam's apple). Keep the tape level and snug but not tight. Record the measurement in centimeters or inches.
- Measure your waist at the navel (belly button) level for men, or at the narrowest point for women. Stand relaxed, do not suck in your stomach. For women, also measure your hips at the widest point of your buttocks.
- Enter your height and weight, then choose your preferred unit system (cm/inches) using the toggle. Fill in all circumference fields and click "Calculate Body Fat" to see your results.
- Review your body fat percentage, fat mass, lean mass, and category on the results panel. Use the composition chart and category range bar to visually understand where you fall. Re-measure every 2-4 weeks to track progress.
Frequently Asked Questions
How accurate is the US Navy body fat method?
The US Navy circumference method is generally accurate within 3-4% of clinical body fat testing methods like DEXA scans. It tends to be most accurate for individuals within normal to moderately overweight ranges. For very lean or very obese individuals, the margin of error may be slightly higher. Despite this, it remains one of the most practical and accessible estimation methods available without specialized equipment.
Why does the formula differ for men and women?
Men and women store fat in different patterns due to hormonal differences. Men tend to accumulate fat primarily around the abdomen, while women store more fat in the hips, thighs, and breasts. The female formula includes a hip measurement to account for this gynoid fat distribution pattern. Women also have higher essential fat levels (10-13%) compared to men (2-5%) due to reproductive biology, so the category thresholds are adjusted accordingly.
What is the best time to take measurements?
For the most consistent results, take your measurements first thing in the morning before eating or drinking. Hydration, recent meals, and exercise can temporarily affect circumference measurements. Always measure on bare skin (not over clothing), stand in a relaxed posture, and use the same measuring positions each time. Taking each measurement twice and using the average improves reliability.
What is a healthy body fat percentage?
Healthy ranges vary by gender and age. For men, 14-24% is generally considered healthy, with athletes typically ranging from 6-13%. For women, 21-31% is considered healthy, with athletes at 14-20%. Essential fat minimums are 2-5% for men and 10-13% for women. Body fat above 25% for men or 32% for women is generally classified as obese and associated with increased health risks including cardiovascular disease and type 2 diabetes.
How is body fat percentage different from BMI?
BMI (Body Mass Index) is a simple ratio of weight to height squared. It does not distinguish between fat and muscle mass. A muscular athlete might have an "overweight" BMI despite having low body fat. Conversely, a person with little muscle mass could have a "normal" BMI but carry excess fat. Body fat percentage directly measures the proportion of fat tissue, providing a more accurate assessment of body composition and health risk.
Can I lower my body fat percentage without losing weight?
Yes, this is called body recomposition. By combining resistance training with adequate protein intake (1.6-2.2 g per kg of body weight), you can build muscle while losing fat simultaneously. Your total body weight may stay the same or even increase slightly, but your body fat percentage will decrease as muscle replaces fat. This process is most effective in beginners, those returning to training after a break, and individuals with higher starting body fat levels.
Why do I need to measure my neck for body fat calculation?
Neck circumference is used in the US Navy formula because it serves as a proxy for lean mass. A larger neck relative to waist size generally indicates more muscle mass and lower body fat. In the mathematical formula, neck circumference is subtracted from waist circumference (and hip for women), which means a thicker neck will yield a lower body fat estimate. This helps the formula account for differences in muscularity between individuals with similar waist measurements.
