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Toolvica

Body Fat Calculator

Estimate your body fat percentage using the U.S. Navy and BMI methods. Free and fast — results are approximations, not clinical measurements.

US UnitsMetric Units
NECKmeasurebelow Adam'sApple
Measurement guidance for this calculator — neck:
in inches
  • Wrap the tape horizontally just below the Adam's apple (larynx), at its narrowest point.
  • Keep the tape snug against the skin — not loose, and not compressing it.
  • Look straight ahead with shoulders relaxed; don't tilt your head or hold your breath.
  • Measure twice and use the same spot each time for consistency.
WAISTat navel levelmeasure
Measurement guidance for this calculator — waist:
in inches
  • For men: measure at navel level. For women: measure at the smallest point between the ribcage and the iliac crest (natural waist).
  • Wrap the tape horizontally and keep it snug against the skin — not loose, and not compressing it.
  • Stand relaxed and breathe normally; don't suck in your stomach or hold your breath.
  • Measure twice and use the same landmark each time for consistency.
Try:

Table of Contents

How to Use the Body Fat Calculator

  1. Select US or Metric units, then choose your gender.
  2. Enter your age and weight. Age is used for the BMI-based fallback, while weight is also used to calculate fat mass and lean body mass.
  3. Enter your height, neck circumference, and waist circumference.
  4. For women, also enter your hip measurement.
  5. Click Calculate to see your body fat percentage, category, and body composition breakdown.
  6. Use the Try buttons for quick examples, or the copy and share buttons to save or send your result.

What is Body Fat Percentage?

Body fat percentage (BFP) is the proportion of fat in your body relative to your total weight. It provides additional information about body composition that weight or BMI alone cannot show, as it distinguishes between fat mass and lean mass (muscle, bone, water).

Essential fat is the minimum amount needed for basic physiological functions — about 2–5% for men and 10–13% for women. Storage fat accumulates in adipose tissue and provides energy reserves and insulation.

While some body fat is essential for health, excess body fat — particularly visceral fat around organs — is associated with increased risks of cardiovascular disease, diabetes, and other conditions.

Measurement Methods

U.S. Navy circumference method

Estimates body fat using the commonly cited U.S. Navy circumference equations, which use the neck, waist, and height (plus hips for women). This calculator is not an official U.S. Navy Body Composition Assessment — the current official procedure uses a different measurement process.

BMI Method

Estimates body fat from BMI and age. Less precise than the Navy method but requires only height and weight. Used as a fallback when required circumference measurements are unavailable or invalid.

How the Body Fat Calculator Works

U.S. Navy circumference equation

The calculator first applies the U.S. Navy circumference equation using your neck, waist, and height (plus hip for women). This is a field estimation method, not a direct measurement — and not an official U.S. Navy Body Composition Assessment. Tape-measure estimates can differ from laboratory body-composition measurements, and measurement technique can affect the result.

BMI-based fallback

If required circumference measurements are unavailable or invalid, the calculator uses a BMI- and age-based estimate instead. The result card tells you which method produced your number.

Fat and lean mass conversion

Your body fat percentage is applied to your total weight to derive fat mass and lean body mass, shown in your selected unit system.

Result categorization

The result is placed into the ACE body fat categories (Essential, Athletes, Fitness, Average, Obese) for men and women for quick interpretation.

View formulas
U.S. Navy circumference equation — Male
%BF = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
U.S. Navy circumference equation — Female
%BF = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
BMI method — Male
%BF = 1.20 × BMI + 0.23 × age − 16.2
BMI method — Female
%BF = 1.20 × BMI + 0.23 × age − 5.4

Age is used by the BMI-based fallback equation; the Navy circumference equations use height and circumference measurements only.

Where waist, neck, hip, and height are measured in centimeters, and age is in years.

Body Fat Categories (ACE)

DescriptionMenWomen
Essential Fat2–5%10–13%
Athletes6–13%14–20%
Fitness14–17%21–24%
Average18–24%25–31%
Obese25+%32+%

Categories shown are based on the American Council on Exercise (ACE) classification and are general reference ranges, not medical diagnoses.

Body-fat category ranges are general reference values and may not account for age, athletic training, pregnancy, or individual health factors.

Frequently Asked Questions

How accurate is the Navy body fat calculator?
The U.S. Navy circumference equation is a field estimation method, not a direct measurement of body fat, and this calculator is not an official U.S. Navy Body Composition Assessment. Tape-measure estimates can differ from laboratory body-composition measurements, and measurement technique can affect the result — sources discussing the method commonly report several percentage points of estimation error relative to reference methods. Accuracy also varies more at high or low body fat levels. For more precise results, consider hydrostatic weighing or DEXA scans.
How do I measure my neck and waist?
For the waist, men should measure at navel level and women at the smallest point between the ribcage and the iliac crest (natural waist) — without sucking in. For the neck, measure horizontally just below the Adam's apple. For women, also measure the hips at the widest point. Use a flexible tape held snug but not compressing the skin, and measure to the nearest ¼ inch.
What is a healthy body fat percentage?
The ACE category table above provides the best reference for healthy ranges by age and sex. Generally, the Athletic and Fitness categories are considered lean and healthy, while the Average category may indicate room for improvement depending on individual goals. Essential fat (the bare minimum for health) is 2–5% for men and 10–13% for women.
Does body fat percentage change with age?
Yes. Body fat tends to increase with age while muscle mass decreases. Ideal body fat percentages gradually rise from the early 20s through the 50s — this is reflected in the ACE category table above and the Jackson & Pollock normative data.
What's the difference between body fat and BMI?
BMI uses only height and weight, so it cannot distinguish between muscle and fat. Body fat percentage directly measures fat, making it more useful for assessing fitness. A muscular person may have a high BMI but low body fat.

References

1. Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy personnel. Research Report 84-26. Naval Health Research Center, 1984.

2. Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Br J Sports Med 1980; 14: 417-424.

3. American Council on Exercise (ACE). ACE Body Fat Categorization.

This calculator provides an estimate, not a clinical measurement. Results can vary with measurement technique and the equation used. For clinical assessment, consult a qualified healthcare professional.

Learn How Body Fat Is Measured

Read our detailed guide on body fat percentage — methods, formulas, healthy ranges, and tips for accurate measurements.

Read the Guide

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