Body Fat Calculator - US Navy Method

Estimate your body fat percentage from tape measurements using the US Navy circumference formula, with category table and lean mass. Free and runs entirely in your browser.

Sex

Units

Measure at the navel.

Estimated body fat

16.4%

Category: Fitness

This is an indication, not medical advice.

Body fat categories (ACE)

CategoryMenWomen
Essential fat2-5%10-13%
Athletes6-13%14-20%
Fitness14-17%21-24%
Average18-24%25-31%
Obese25%+32%+

How the US Navy Body Fat Method Works

The US Navy circumference method, developed by Hodgdon and Beckett at the Naval Health Research Center in 1984, estimates body fat from just a tape measure. For men it uses height, neck, and waist; for women it adds the hip measurement because women store proportionally more fat around the hips. The formula converts these circumferences through logarithms into a body density estimate and then into a fat percentage. Against underwater weighing it is accurate to within about 3-4 percentage points for most people.

Measurement technique matters more than the math. Use a flexible, non-stretch tape held snug but not compressing the skin. Men measure the waist horizontally at the navel; women at the narrowest point of the torso and hips at the widest point. Measure the neck just below the larynx, sloping slightly downward to the front. Take each measurement two or three times in the morning before eating and use the average, since a single sloppy measurement can swing the result by two points or more.

The category table comes from the American Council on Exercise. For men, 2-5% is essential fat, 6-13% typical for athletes, 14-17% fit, 18-24% average, and 25%+ classified as obese. For women the bands sit roughly 8-10 points higher because essential fat requirements are greater: 10-13% essential, 14-20% athletes, 21-24% fitness, 25-31% average, 32%+ obese. Body fat percentage is generally a better health signal than BMI alone, since BMI cannot separate a muscular 90 kg from a sedentary 90 kg.

If you also enter your weight, the calculator splits it into fat mass and lean mass (muscle, bone, organs, water). Tracking lean mass during a diet tells you whether you are losing fat or muscle: losing 3 kg while lean mass holds steady is a win, losing 3 kg of which 2 kg is lean mass is a warning to raise protein and keep lifting. Pair this tool with the Macro Calculator to set protein targets and the BMI Calculator for a complementary baseline.

How the Body Fat Calculator Works

  1. 01Select your sex and unit system (cm/kg or inches/lb).
  2. 02Measure and enter your height, neck, and waist; women also enter hip circumference.
  3. 03Optionally enter your weight to see lean mass and fat mass.
  4. 04The US Navy formula estimates your body fat percentage and shows your ACE category.

Measuring Correctly

Use a flexible, non-stretch tape held snug but not compressing the skin, ideally in the morning before eating. Men measure the waist horizontally at the navel; women measure the waist at the narrowest point of the torso and the hips at the widest point. Measure the neck just below the larynx. Take each measurement two or three times and average them; a single sloppy measurement can shift the result by two percentage points. The US Navy method is typically accurate within 3-4 points of underwater weighing.

When to Use This Calculator

Use it as a monthly progress check during a diet or muscle-building phase, where the direction of change matters more than the absolute number. It is more informative than the scale alone: combined with your weight it splits the change into fat mass and lean mass, telling you whether a diet is burning fat or costing muscle. It is also a better health screen than BMI for muscular people, whom BMI often misclassifies as overweight.

Common Use Cases

Tips

  • Measure at the same time of day under the same conditions; mornings before breakfast are most repeatable.
  • Average two or three tape readings per site; the formula is only as good as the measurements.
  • Compare your own trend over months rather than your number against other people; between-person error is larger than within-person error.

Frequently Asked Questions

How accurate is the US Navy method?→
Studies put it within about 3-4 percentage points of laboratory methods like underwater weighing for most people, which is comparable to consumer bioimpedance scales. Accuracy depends heavily on measuring technique, so consistent tape placement matters more than the formula.
What is a healthy body fat percentage?→
Per the ACE classification, the fitness range is 14-17% for men and 21-24% for women, with the average range extending to 24% and 31% respectively. Women naturally carry roughly 8-10 points more fat than men because essential fat requirements are higher.
Why do women need a hip measurement?→
The formula was calibrated separately per sex. Women store proportionally more fat around the hips and thighs, so adding hip circumference significantly improves accuracy; for men, waist and neck alone predict body density well enough.
What is lean mass?→
Lean mass is everything that is not fat: muscle, bone, organs, and water. If you enter your weight, the calculator splits it into fat mass and lean mass. Tracking lean mass during weight loss shows whether you are preserving muscle; if it drops fast, raise protein and keep strength training.
Can body fat be too low?→
Yes. Essential fat, about 2-5% for men and 10-13% for women, is required for hormone production, insulation, and organ protection. Sustained levels below that range cause serious health problems, which is why even competitive bodybuilders only touch such levels briefly.

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