How does the Navy body fat method work?

The U.S. Navy method estimates body fat percentage from circumference measurements — neck and waist for men, plus hip for women — combined with height. It uses a logarithmic formula validated against underwater weighing and is generally more accurate than BMI-based estimates because it accounts for where weight is actually carried.

How accurate is the Navy method?

Studies comparing the Navy method to DEXA scans and hydrostatic weighing typically show it within 3-4% of the true value for most people, making it one of the more accurate methods that only requires a tape measure. Accuracy depends heavily on measuring each site correctly and consistently.

What's the difference between the Navy method and the BMI method?

The Navy method uses body circumference measurements and is more accurate because it reflects where fat is actually distributed. The BMI method (Deurenberg formula) only uses height, weight, age, and sex, so it can't distinguish muscle from fat — a muscular person will show a higher BMI-based body fat estimate than they actually have.

How do I measure my neck, waist, and hip correctly?

Measure your neck just below the larynx (Adam's apple), tilting slightly down. Measure your waist at the narrowest point, usually at the navel level. Measure hips at the widest point around the buttocks. Keep the tape snug but not compressing the skin, and measure at the same time of day for consistency.

What is a healthy body fat percentage?

For men, 14-24% is generally considered the healthy 'fitness' to 'average' range, with athletes often in the 6-13% range. For women, 21-31% is generally considered healthy, with athletes often in the 14-20% range. Essential fat (the minimum needed for basic health) is about 2-5% for men and 10-13% for women.

What are fat mass and lean body mass?

Fat mass is the portion of your total weight made up of body fat, calculated as your weight multiplied by your body fat percentage. Lean body mass is everything else — muscle, bone, organs, and water. Tracking both over time can be more useful than tracking weight alone, since weight doesn't reveal what's actually changing.

Why does body fat percentage vary so much by age and sex?

Women naturally carry more essential fat than men to support reproductive function, which is why healthy ranges run about 8-10 percentage points higher for women at every age. Body fat also tends to rise gradually with age for both sexes as muscle mass declines, which is reflected in the age-banded ideal ranges shown in your results.

Can I use this calculator to track fat loss progress?

Yes — re-measuring every 2-4 weeks with the Navy method is a practical way to track body composition changes without expensive equipment. Because the formula is sensitive to measurement technique, measure at the same time of day, in the same way, each time for the most consistent trend.

Is this calculator a substitute for a DEXA scan or medical assessment?

No. DEXA scans, hydrostatic weighing, and bod pod testing directly measure body composition and are more accurate than any tape-measure or formula-based method. This calculator gives a fast, free estimate — this is an estimate only and not a medical diagnosis.

Body Fat Calculator

Estimate your body fat percentage using the U.S. Navy method or BMI method, plus fat mass, lean body mass, and your ideal healthy range.

Age (years)

Height (cm)

Weight (kg)

Neck (cm)

Waist (cm)

Body Fat % (Navy Method)

16.4 %

Fitness

Body Fat % (BMI method)

21.0%

BMI

25.2

Fat mass

13.1 kg

Lean body mass

66.9 kg

Ideal range (male, age-matched)

8% – 19%

To reach healthy range

Already in range

This is an estimate only and not a medical diagnosis.

How to use the body fat calculator

1
Select your sex and metric or imperial units.
2
Enter your age, height, and weight.
3
Enter your neck and waist circumference (plus hip circumference for women) to unlock the more accurate Navy method.
4
Your body fat percentage, category, fat mass, lean mass, and ideal range update instantly.

How the Navy and BMI methods work

U.S. Navy method (primary): Developed by the U.S. Navy as a fast, equipment-free alternative to underwater weighing, this method uses circumference measurements and a logarithmic formula. Men: %BF = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. Women: %BF = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450, with all measurements in centimeters.

BMI method (secondary): When circumference measurements aren't available, we fall back to the Deurenberg formula, which estimates body fat from BMI, age, and sex: %BF = 1.2 × BMI + 0.23 × age − 10.8 × (1 for male, 0 for female) − 5.4. It's less accurate than the Navy method because it can't distinguish muscle from fat, but it needs only height, weight, age, and sex.

Fat mass and lean body mass: Fat mass = body weight × body fat percentage. Lean body mass = body weight − fat mass. Lean mass includes muscle, bone, organs, and water.

Once you have your body fat percentage, pairing it with your BMI gives a fuller picture — and if your goal is to change your body composition, our TDEE & BMR calculator turns that goal into a daily calorie target.

Body fat categories explained

Body fat categories describe where your percentage falls relative to essential fat, athletic conditioning, general fitness, and average population ranges. These categories are gender-specific because women carry more essential fat than men for reproductive health.

Category	Men	Women
Essential Fat	2-5%	10-13%
Athletes	6-13%	14-20%
Fitness	14-17%	21-24%
Average	18-24%	25-31%
Obese	25%+	32%+

Your "ideal range" result uses commonly-referenced healthy body fat bands by age group, since healthy ranges shift gradually upward with age for both sexes. If your result falls outside that range, the calculator estimates the approximate weight you'd need to lose or gain — assuming your lean body mass stays constant — to land back inside it.

Frequently asked questions

Step-by-step guide to the U.S. Navy body fat formula, how to measure neck, waist, and hip correctly, and why it beats BMI for estimating body composition.

Read the guide →

Body Fat Percentage vs. BMI: Which Should You Trust?

How body fat percentage and BMI differ, why they can disagree for the same person, and when each measurement is actually the more useful one.

Read the guide →

Body Fat Calculator Guide: Reading Your Full Results

What each result from the body fat calculator means — fat mass, lean body mass, category, and ideal range — and how to use them to set a real target.

Read the guide →