# What is my body fat?

Estimates body fat percentage with the U.S. Navy tape-measure equations or the Deurenberg BMI equation, with fat mass, lean mass, and the ACE category.

- Page: https://www.acalculator.org/health/body-fat-calculator
- JSON spec: https://www.acalculator.org/health/body-fat-calculator.json
- Version: 7f08129e20dc

## Default answer

Example with the default inputs (Method U.S. Navy (tape measure), Sex Male, Age 30, Height 5 ft 10 in, Weight 180 lb, Waist 32 in, Neck 16 in): Your estimated body fat is 11.1%, in the ACE Athletes range.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| method | Method | The equation used: U.S. Navy tape measurements, or BMI with age and sex. |
| sex | Sex | Sex at birth, which the body formulas use. |
| age | Age | Your age in whole years. Only the BMI method uses it. |
| height | Height | Your height without shoes. |
| bodyWeight | Weight | Your body weight, for fat mass and lean mass (and BMI in the BMI method). |
| waistCirc | Waist | Waist circumference: at the navel for men, at the narrowest point for women. |
| neckCirc | Neck | Neck circumference, just below the larynx (Adam’s apple). |
| hipCirc | Hip | Hip circumference at the widest point. Women only. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| bodyFat | Body fat | Estimated body fat as a percent of body weight. |
| category | ACE category | The American Council on Exercise category for this body fat percentage and sex. |
| leanShare | Lean share | Lean body mass as a percent of body weight: 100 − body fat percent. |
| fatMass | Fat mass | Body weight × body fat percent. |
| leanMass | Lean body mass | Body weight minus fat mass. |
| bmi | BMI | Body mass index, weight in kg ÷ height in m squared (the BMI method uses it). |

## Method

U.S. Navy (DoD), inches: men %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76; women %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. BMI method (Deurenberg 1991): %BF = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex 1 for men, 0 for women).

## Assumptions

- The Navy equations take circumferences and height in inches; the calculator converts centimetres first (1 in = 2.54 cm).
- Categories are the American Council on Exercise (ACE) ranges, lower bound inclusive.
- The equations are for adults. They estimate body fat; lab methods such as DEXA measure it.

## Worked examples

1. method = navy, sex = male, age = 30, height = 1.778, bodyWeight = 81.646627, waistCirc = 0.8128, neckCirc = 0.4064 gives bodyFat = 11.093848%, category = Athletes, fatMass = 9.057753.
2. method = navy, sex = female, age = 30, height = 1.651, bodyWeight = 63.502932, waistCirc = 0.762, neckCirc = 0.3302, hipCirc = 1.016 gives bodyFat = 31.087927%, category = Average.
3. method = navy, sex = male, age = 40, height = 1.8, bodyWeight = 85, waistCirc = 0.9, neckCirc = 0.4 gives bodyFat = 18.462079%, category = Average, leanMass = 69.307233.
4. method = bmi, sex = male, age = 30, height = 1.778, bodyWeight = 81.646627 gives bodyFat = 21.692455%, bmi = 25.827046, category = Average. Source: Deurenberg et al. (1991): 1.20 × BMI 25.83 + 0.23 × 30 − 10.8 × 1 − 5.4 = 21.69%.
5. method = bmi, sex = female, age = 45, height = 1.6, bodyWeight = 64 gives bodyFat = 34.95%, category = Obese. Source: Deurenberg et al. (1991): BMI 64 ÷ 1.6² = 25.

## FAQ

### How does the body fat calculator work?

The calculator applies established formulas to estimate body fat. The U.S. Navy method uses log-based equations with waist, neck, and height for men, and waist, hip, neck, and height for women. The BMI method uses BMI, age, and sex (the Deurenberg formula). Both show fat mass (weight × body fat percent) and lean body mass (weight minus fat mass).

### What is a healthy body fat percentage?

Healthy body fat ranges differ by sex. According to the American Council on Exercise (ACE): Essential fat: Men 2–5%, Women 10–13%; Athletes: Men 6–13%, Women 14–20%; Fitness: Men 14–17%, Women 21–24%; Average: Men 18–24%, Women 25–31%; Obese: Men ≥25%, Women ≥32%.

### Why does body fat percentage matter?

Monitoring body fat is more meaningful than weight alone. Two people with the same weight can have very different body compositions. Body fat percentage directly reflects how much fat you carry, helping you track fat loss versus muscle gain. Excess fat, especially visceral fat, is linked to higher risk of heart disease, diabetes, and other conditions.

### How accurate is this calculator?

This calculator provides an estimate based on population averages. For clinical precision, lab methods like DEXA or hydrostatic weighing are better. For home use, this calculator is convenient and consistent for tracking trends over time.

### How do I measure correctly?

Height: Stand straight without shoes. Weight: Use a reliable scale. Waist: men measure at the navel while relaxed; women measure at the narrowest point of the waist. Neck: Measure just below the Adam's apple. Hip (women): Measure around the widest part of the hips. Use a non-stretch tape on bare skin. Don't squeeze the tape too tightly or hold your breath. Measure first thing in the morning for consistency.

### What is Lean Body Mass?

Lean Body Mass (LBM) is everything except fat: muscle, organs, bone, water, etc. Our calculator shows LBM in pounds or kg. Maintaining LBM is important for metabolism and strength.

### How often should I check my body fat?

It's best to check monthly rather than daily to see real changes. Always measure under similar conditions (e.g. morning, before meals).

### Can I use this calculator at any age?

The formulas are generally for adults. For children, teens, or older adults, consult a professional. Norms are mostly based on younger adults.

### Is low body fat always better?

No. Essential fat is needed for hormone and organ function. Excessively low body fat can be unhealthy. Always interpret your number along with how you feel and under medical guidance.

## Sources

- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Reports 84-11 and 84-29, San Diego, 1984.
- U.S. Army Regulation 600-9, The Army Body Composition Program (DoD circumference equations, in inches).
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr. 1991;65(2):105-114. https://doi.org/10.1079/bjn19910073
- American Council on Exercise, Percent Body Fat Calculator (body fat categories). https://www.acefitness.org/resources/everyone/tools-calculators/percent-body-fat-calculator/