Body Fat Calculator
Calculate your body fat percentage, fat mass, and lean mass using the U.S. Navy circumference method
What Is Body Fat Percentage?
Body fat percentage is the proportion of fat to total body weight. It is a better indicator of health and fitness than BMI because it distinguishes between fat and lean tissue like muscle and bone. This calculator uses the U.S. Navy circumference method, which estimates body fat from a few simple tape-measure readings.
How the Navy Method Works
The Navy method uses a regression formula based on neck, waist (and for women, hip) circumference along with height. This calculator uses the metric version of the formula, converting any inch-based measurements to centimeters internally so results stay consistent regardless of which unit you enter.
Men: Body Fat % = 495 ÷ [1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)] − 450
Women: Body Fat % = 495 ÷ [1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)] − 450
All measurements are in centimeters.
Explanation of Every Input
Gender
Men and women use different regression equations because body fat tends to distribute differently between the sexes, so accurate results depend on selecting the correct one.
Height, Neck & Waist
Height is measured standing without shoes; neck is measured just below the larynx; waist is measured at the narrowest point, or at the navel if there is no natural narrowing.
Hip (Women Only)
Hip circumference, measured at the widest point of the buttocks, is required for the female formula and improves accuracy for typical female fat distribution.
Weight
Your total body weight is used only to convert body fat percentage into concrete fat mass and lean mass figures in kilograms or pounds.
Body Fat Categories
Essential Fat (Men 2-5%, Women 10-13%)
The minimum fat needed for basic bodily functions. Not recommended to sustain long-term.
Athletes (Men 6-13%, Women 14-20%)
Typical range for fitness enthusiasts and competitive athletes.
Fitness (Men 14-17%, Women 21-24%)
Good fitness level with visible muscle definition.
Average (Men 18-24%, Women 25-31%)
An acceptable range for most of the general population.
Obese (Men 25%+, Women 32%+)
Associated with a higher risk of health problems; lifestyle changes are often recommended.
How to Measure Accurately
- Use a flexible, non-stretch tape measure.
- Keep the tape snug against the skin without compressing it.
- Measure at the same time of day, ideally before eating.
- Take each measurement 2-3 times and use the average.
Advantages of Using This Calculator
- No special equipment needed — just a tape measure.
- Converts your result into concrete fat mass and lean mass figures.
- Supports both metric and imperial units.
- Shows exactly where your result sits against standard category ranges.
Limitations
- Less precise than lab methods like DEXA scans or hydrostatic weighing.
- Sensitive to measurement technique — inconsistent measuring reduces accuracy.
- Does not account for age, ethnicity, or individual fat distribution differences.
Common Mistakes to Avoid
- Measuring over clothing instead of directly on skin.
- Pulling the tape too tight, which understates circumference.
- Comparing results measured at different times of day or hydration levels.
- Forgetting to switch units consistently when entering measurements.
Worked Examples
Athletic Male
Profile: Male, 175 cm, Neck 38 cm, Waist 80 cm, Weight 75 kg
Body Fat: 12.9%
Category: Athletes
Fat Mass: 9.7 kg
Lean Mass: 65.3 kg
A relatively small waist-to-neck difference for this height produces a low body fat estimate, placing this profile in the Athletes range.
Average Male
Profile: Male, 178 cm, Neck 40 cm, Waist 95 cm, Weight 90 kg
Body Fat: 22.2%
Category: Average
Fat Mass: 20.0 kg
Lean Mass: 70.0 kg
A larger waist relative to neck and height pushes this estimate into the Average category, common for a generally active but non-athletic build.
Fitness-Level Woman
Profile: Female, 165 cm, Neck 32 cm, Waist 70 cm, Hip 95 cm, Weight 65 kg
Body Fat: 24.8%
Category: Fitness
Fat Mass: 16.1 kg
Lean Mass: 48.9 kg
This combination of measurements sits right at the edge of the Fitness range for women, just under the Average threshold.
Average-Range Woman
Profile: Female, 160 cm, Neck 33 cm, Waist 85 cm, Hip 105 cm, Weight 75 kg
Body Fat: 38.0%
Category: Obese
Fat Mass: 28.5 kg
Lean Mass: 46.5 kg
A larger waist and hip measurement relative to neck and height produces a much higher estimate, illustrating how sensitive the formula is to these circumference differences.
Frequently Asked Questions
How accurate is the Navy body fat method?
The U.S. Navy circumference method is generally considered accurate within about 3-4% of body fat compared to more expensive lab methods like DEXA scans or hydrostatic weighing. It is far more accessible than lab testing while still being considerably more informative than BMI alone.
Why does the calculator ask for hip measurement only for women?
The Navy formula uses different regression equations for men and women because fat is typically distributed differently between the sexes. The female equation includes hip circumference because it improves accuracy for the way women tend to store body fat.
What is the difference between body fat percentage and BMI?
BMI only considers height and total weight, so it cannot distinguish between muscle and fat — a muscular person can be classified as "overweight" by BMI despite low body fat. Body fat percentage measures the actual proportion of fat to total body mass, making it a more meaningful indicator of health and fitness.
What is essential fat and why is it important?
Essential fat is the minimum amount of body fat needed for basic physiological functions like hormone production, organ protection, and nutrient absorption — roughly 2-5% for men and 10-13% for women. Falling below essential fat levels for extended periods can be harmful to health.
What are fat mass and lean mass?
Fat mass is the total weight of fat tissue in your body, calculated by multiplying your body fat percentage by your total weight. Lean mass is everything else — muscle, bone, organs, and water — calculated as your total weight minus fat mass.
How do I measure my neck, waist, and hip accurately?
Measure your neck just below the larynx (Adam's apple), your waist at the narrowest point (or at the navel if there is no natural narrowing), and — for women — your hips at the widest point of the buttocks. Keep the tape measure snug but not compressing the skin, and measure at the same time of day for consistent tracking.
How often should I re-measure my body fat percentage?
Body fat changes slowly, so re-measuring every 2-4 weeks under similar conditions (same time of day, similar hydration) gives a more meaningful trend than measuring daily, which mostly reflects water weight fluctuation.
Can I use inches instead of centimeters?
Yes — use the Measurement Unit option in Advanced Options to switch to inches for height, neck, waist, and hip, and switch Weight Unit to pounds if preferred. The calculator converts everything internally so the result is identical regardless of which units you enter.
Why is my waist measurement close to or smaller than my neck measurement?
The formula for men requires waist to be larger than neck (and for women, waist plus hip larger than neck), since it is based on the difference between these measurements. If your values do not satisfy this, double check your measurements — a waist smaller than neck usually indicates a measurement error.
Is a very low body fat percentage always healthy?
Not necessarily — extremely low body fat, especially below essential fat levels, can disrupt hormone production, immune function, and other bodily processes. The healthiest range depends on your goals, sex, and activity level, and very lean physiques are usually only sustained short-term by competitive athletes.
How does body fat percentage change with weight loss?
Losing weight through a calorie deficit typically reduces both fat mass and some lean mass, though resistance training and adequate protein intake help preserve more lean mass during the process. Re-measuring periodically shows whether your loss is coming primarily from fat, which is the healthier outcome.
Does this calculator account for age or ethnicity?
No — the Navy method uses only circumference measurements and height, so age and ethnicity are not factored in directly. Some other formulas do include age as a variable, which can produce slightly different estimates for the same measurements.
Conclusion
Body fat percentage tells a more complete story about your health and fitness than weight or BMI alone. Use this calculator every few weeks with consistent measurement technique to track real changes in fat mass and lean mass over time.