How to Calculate Body Fat Percentage (Navy Method)

Body fat percentage tells you what fraction of your total body weight is fat tissue versus lean mass (muscle, bone, organs, water). Unlike BMI, which only looks at height and weight, body fat percentage gives a more direct picture of body composition. Two people can weigh the same amount but have vastly different body fat levels, different health risk profiles, and different appearances.

This guide explains the U.S. Navy circumference method in detail, walks through the math with examples, and compares it to other measurement approaches. For instant results, try our Body Fat Calculator.

Medical Disclaimer: Body fat estimates from circumference measurements are approximations with a typical error margin of 3-4%. They should not replace clinical body composition analysis. Consult a healthcare provider for medical assessments or if you have concerns about your body composition.

The U.S. Navy Method Explained

The U.S. Navy developed this circumference-based method to assess the body composition of military personnel without requiring lab equipment. It uses a logarithmic formula based on specific body measurements and was validated against hydrostatic (underwater) weighing.

Measurements Needed

For men:

• Waist circumference (at navel level)
• Neck circumference (just below the larynx)
• Height

For women:

• Waist circumference (at the narrowest point)
• Neck circumference (just below the larynx)
• Hip circumference (at the widest point)
• Height

The Formulas

All measurements in inches (or centimeters with metric conversion). The formulas use base-10 logarithms.

For men:

$Body \ Fat \ \% = 86.010 \times \log_{10}(waist - neck) - 70.041 \times \log_{10}(height) + 36.76$

For women:

$Body \ Fat \ \% = 163.205 \times \log_{10}(waist + hip - neck) - 97.684 \times \log_{10}(height) - 78.387$

Worked Example (Male)

A man with a waist of 36 inches, neck of 15.5 inches, and height of 71 inches.

1. Waist minus neck: 36 - 15.5 = 20.5
2. Log10(20.5) = 1.3118
3. Log10(71) = 1.8513
4. Body fat % = (86.010 x 1.3118) - (70.041 x 1.8513) + 36.76
5. = 112.83 - 129.65 + 36.76
6. = 19.9%

Worked Example (Female)

A woman with a waist of 30 inches, hip of 39 inches, neck of 13 inches, and height of 65 inches.

1. Waist plus hip minus neck: 30 + 39 - 13 = 56
2. Log10(56) = 1.7482
3. Log10(65) = 1.8129
4. Body fat % = (163.205 x 1.7482) - (97.684 x 1.8129) - 78.387
5. = 285.38 - 177.07 - 78.387
6. = 29.9%

Body Fat Categories

The American Council on Exercise (ACE) defines these general body fat ranges:

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%+

From our examples: the male at 19.9% falls in the “average” range, and the female at 29.9% also falls in the “average” range for women.

Essential fat is the minimum amount needed for normal physiological function. It cushions organs, insulates nerves, regulates hormones, and enables vitamin absorption. Dropping below essential fat levels causes serious health consequences including hormonal disruption, bone loss, organ damage, and immune system failure.

How to Take Accurate Measurements

The accuracy of the Navy method depends entirely on consistent, correct measurements. Sloppy measuring technique is the primary source of error.

General Rules

• Time of day: Measure first thing in the morning, before eating or drinking, after using the bathroom. Body measurements fluctuate throughout the day due to food, water, and gravity.
• Tool: Use a flexible cloth or fiberglass tape measure. Avoid metal tapes.
• Tension: Pull the tape snug against the skin without compressing it. You should be able to slide a finger under the tape.
• Repetition: Take each measurement three times and average the results.
• Posture: Stand upright with weight evenly distributed on both feet. Do not suck in your stomach.

Specific Measurement Points

Neck: Measure just below the larynx (Adam’s apple) with the tape sloping slightly downward at the front. Do not flex your neck muscles.

Waist (men): Measure at the navel (belly button) level. Keep the tape horizontal all the way around.

Waist (women): Measure at the narrowest point of the torso, typically between the bottom of the rib cage and the top of the hip bone.

Hips (women): Measure at the widest point of the buttocks/hips with feet together.

Tracking Over Time

Individual readings matter less than trends. Even if your absolute body fat percentage is off by 2-3% due to measurement limitations, tracking changes over weeks and months using the same method and technique gives you reliable directional information. If your Navy method result goes from 25% to 22% over three months, you have genuinely lost fat regardless of whether the starting point was actually 23% or 27%.

Comparing Body Fat Measurement Methods

No method outside of a cadaver dissection measures body fat with perfect accuracy. Each approach has tradeoffs between precision, cost, and accessibility.

DEXA Scan (Dual-Energy X-ray Absorptiometry)

• Accuracy: Within 1-2% of true body fat
• Cost: $50-150 per scan
• Availability: Medical facilities, some gyms and wellness clinics
• Pros: Gold standard for practical use, also measures bone density and shows regional fat distribution
• Cons: Slight radiation exposure (less than a cross-country flight), requires appointment, cost adds up for regular tracking

Skinfold Calipers

• Accuracy: Within 3-4% when done by a skilled technician
• Cost: $10-30 for calipers, or included with trainer sessions
• Availability: Gyms, personal trainers, clinics
• Pros: Inexpensive, portable, can track changes in specific body regions
• Cons: Highly dependent on the technician’s skill and pinch site accuracy. Different practitioners will get different results on the same person.

Hydrostatic (Underwater) Weighing

• Accuracy: Within 1-2%
• Cost: $40-80 per test
• Availability: University labs, some fitness centers
• Pros: Very accurate, long research history
• Cons: Requires full submersion in a tank while exhaling completely, which is uncomfortable. Less available than DEXA.

Bioelectrical Impedance Analysis (BIA)

• Accuracy: Within 3-8% depending on device quality
• Cost: $20-60 for a home scale, or free at some gyms
• Availability: Consumer scales, handheld devices, gym equipment
• Pros: Extremely convenient, many smart scales include it
• Cons: Heavily affected by hydration, food intake, and skin temperature. Results can swing 3-5% within the same day depending on when you measure.

Navy Circumference Method

• Accuracy: Within 3-4%
• Cost: Free (just a tape measure)
• Availability: Anywhere
• Pros: No equipment beyond a tape measure, easy to do at home, consistent when technique is controlled
• Cons: Assumes typical fat distribution patterns, less accurate for individuals who carry fat differently than average

Limitations of the Navy Method

The Navy formula was developed using U.S. military personnel, a population that skews younger, more physically active, and more male. Several limitations follow:

• Fat distribution: The formula assumes a correlation between circumference measurements and total body fat. People who carry disproportionate fat in areas not measured (arms, back, thighs) may get inaccurate results.
• Muscular individuals: A person with a large, muscular neck and narrow waist could get an unrealistically low body fat reading.
• Very lean individuals: At very low body fat levels (below 10% for men, below 18% for women), circumference-based estimates lose precision.
• Age: The formula doesn’t include an age variable, even though fat distribution shifts with aging.

Despite these limitations, the Navy method remains one of the most practical free options for estimating and tracking body fat percentage at home.

Skip the Math

Our Body Fat Calculator runs the Navy method instantly. Enter your measurements and get your estimated body fat percentage with the corresponding ACE category.

Frequently Asked Questions

How often should I measure my body fat percentage?

Every 2-4 weeks is a reasonable frequency for tracking changes. Body fat doesn’t shift dramatically from day to day, and more frequent measurements tend to introduce noise from measurement variation rather than reflecting real changes. Always measure under the same conditions (same time of day, same hydration state, same technique) for the most meaningful comparisons.

What body fat percentage shows visible abs?

For most men, abdominal muscles become visible around 10-14% body fat, with clear definition at 8-12%. For women, visible abs typically appear around 16-20% body fat. These numbers vary based on genetics, where you store fat, and how developed your abdominal muscles are. A person with well-developed abs may see definition at a higher body fat percentage than someone with less abdominal muscle mass.

Is body fat percentage more important than BMI?

Body fat percentage provides more useful information about health risk and body composition than BMI, because it directly measures what matters: how much of your weight is fat versus lean tissue. However, it’s harder to measure accurately. In clinical practice, BMI remains the standard screening tool because it requires only a scale and a height measurement. The best approach is to consider both metrics alongside waist circumference and other health markers.

Can body fat percentage be too low?

Absolutely. Essential body fat (2-5% for men, 10-13% for women) is necessary for survival. Dropping below these levels disrupts hormone production, weakens the immune system, impairs organ function, and reduces bone density. Female athletes who maintain very low body fat often experience amenorrhea (loss of menstrual periods), which is linked to bone stress fractures and long-term osteoporosis. Competitive bodybuilders reach extremely low body fat for brief competition appearances, not as a sustainable lifestyle.

Why does the Navy method need a neck measurement?

Neck circumference serves as a proxy for lean body mass in the formula. A larger neck relative to waist size correlates with more muscle mass and lower body fat. The formula uses the difference between waist and neck (for men) or the sum of waist and hip minus neck (for women) to estimate the ratio of fat to lean tissue. Without the neck measurement, the formula would overestimate body fat in muscular individuals.