Body Fat Calculator — Free Online Body Fat Percentage Tool
Estimate your body fat percentage using the US Navy circumference method. Get your body fat category, fat mass, and lean mass breakdown with metric or imperial measurements.
Body Fat Results (US Navy Method)
Acceptable
Body Fat Categories (Male)
Summary: Your estimated body fat is 23.5%, categorized as Acceptable. This is an estimate based on the US Navy circumference method. DEXA scans and hydrostatic weighing provide more precise measurements.
How to Use the Body Fat Calculator
- Select your unit system: Choose Metric (centimeters) or Imperial (inches) using the toggle. All measurement fields adjust automatically to your chosen system.
- Select your biological sex: The calculator uses sex-specific formulas because fat distribution differs between males and females. The female formula requires an additional hip measurement.
- Enter your body weight: Input your current weight in kilograms or pounds. Weigh yourself at a consistent time of day for the most reliable tracking over time.
- Enter your height: Input your height in centimeters or feet and inches. Stand straight without shoes for the most accurate measurement.
- Measure and enter circumferences: Using a flexible tape measure, input your waist circumference (measured at navel level), neck circumference (measured just below the larynx), and for females, hip circumference (measured at the widest point of the buttocks). Keep the tape snug but not compressing the skin, and measure at the end of a normal breath.
- Review your results: The calculator instantly shows your estimated body fat percentage, body fat category, total fat mass, and lean body mass. The category ranges adjust automatically based on your selected sex.
For the most consistent tracking over time, always measure circumferences at the same anatomical landmarks, at the same time of day, and in a similar state of hydration.
US Navy Body Fat Formula
Male Formula:
BF% = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76 Female Formula:
BF% = 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387 Variables Explained
- Waist: Circumference in centimeters, measured at the navel for females and at the narrowest point for males. This is the primary predictor of abdominal fat.
- Neck: Circumference in centimeters, measured just below the larynx (Adam's apple). This serves as a proxy for upper body lean mass.
- Hip (female only): Circumference at the widest point of the buttocks. This accounts for the sex-specific fat distribution in the gluteal region.
- Height: Total height in centimeters. Taller individuals tend to have proportionally different fat distributions.
- log10: The base-10 logarithm function. It linearizes the relationship between circumference measurements and body fat percentage.
Step-by-Step Calculation Example (Male)
A male with waist 90 cm, neck 38 cm, and height 178 cm:
- Waist minus neck: 90 - 38 = 52 cm
- log10(52) = 1.7160
- log10(178) = 2.2504
- 86.010 x 1.7160 = 147.59
- 70.041 x 2.2504 = 157.61
- Body fat: 147.59 - 157.61 + 36.76 = 26.7%
At 26.7%, this falls in the Obese category for males (25%+). If the individual weighs 85 kg, fat mass is approximately 22.7 kg and lean mass is 62.3 kg.
Practical Examples
Example 1: Marcus Tracking Fitness Progress
Marcus is a 32-year-old who has been following a strength training program for 3 months. He weighs 82 kg, stands 180 cm, with a waist of 82 cm and neck of 39 cm:
- Body Fat: 86.010 x log10(82-39) - 70.041 x log10(180) + 36.76 = 19.3%
- Category: Acceptable (18-24% for males)
- Fat Mass: 82 x 0.193 = 15.8 kg
- Lean Mass: 82 - 15.8 = 66.2 kg
Marcus's body fat of 19.3% is in the acceptable range. By tracking monthly, he can monitor whether his training program is reducing fat while maintaining or building lean mass, even if his scale weight stays similar.
Example 2: Diana's Wellness Assessment
Diana is a 45-year-old teacher weighing 68 kg at 165 cm, with waist 76 cm, neck 32 cm, and hip 98 cm:
- Body Fat: 163.205 x log10(76+98-32) - 97.684 x log10(165) - 78.387 = 29.8%
- Category: Acceptable (25-31% for females)
- Fat Mass: 68 x 0.298 = 20.3 kg
- Lean Mass: 68 - 20.3 = 47.7 kg
Diana's body fat of 29.8% is within the acceptable range for women. Her doctor notes this is a healthy percentage for her age and advises maintaining her current activity level.
Example 3: Ryan Preparing for Athletic Season
Ryan is a 22-year-old collegiate swimmer weighing 78 kg at 183 cm, with waist 76 cm and neck 40 cm:
- Body Fat: 86.010 x log10(76-40) - 70.041 x log10(183) + 36.76 = 12.2%
- Category: Athlete (6-13% for males)
- Fat Mass: 78 x 0.122 = 9.5 kg
- Lean Mass: 78 - 9.5 = 68.5 kg
Ryan's 12.2% body fat reflects his athletic training regimen. His sports nutritionist uses this data along with performance metrics to ensure he maintains sufficient energy reserves for competitive swimming while staying in peak condition.
Body Fat Percentage Reference Table
| Category | Male Range | Female Range | Description |
|---|---|---|---|
| Essential Fat | 2-5% | 10-13% | Minimum for basic physiological function |
| Athlete | 6-13% | 14-20% | Typical of competitive athletes |
| Fitness | 14-17% | 21-24% | Lean and fit body composition |
| Acceptable | 18-24% | 25-31% | Healthy range for general population |
| Obese | 25%+ | 32%+ | Excess body fat with increased health risks |
Tips and Complete Guide to Body Fat Assessment
Understanding Body Fat Distribution
Where your body stores fat matters as much as how much you carry. Visceral fat, stored deep around abdominal organs, is metabolically active and strongly associated with increased risk of type 2 diabetes, cardiovascular disease, and certain cancers. Subcutaneous fat, stored beneath the skin, is less metabolically dangerous. The US Navy method captures abdominal fat distribution through waist circumference, making it a useful screening tool for cardiometabolic risk. People with higher waist circumferences relative to their hips (apple-shaped distribution) tend to have greater health risks than those who store fat in the hips and thighs (pear-shaped distribution).
How Age Affects Body Fat
Body fat percentage naturally increases with age, even if body weight remains stable. This occurs because lean muscle mass decreases by approximately 3-8% per decade after age 30 (a process called sarcopenia), and is replaced by fat tissue. Hormonal changes during menopause for women and declining testosterone in men accelerate this process. This means the same body fat percentage may carry different health implications at age 25 versus age 55. Regular resistance training and adequate protein intake are the most effective strategies for preserving lean muscle mass and maintaining a healthy body fat percentage as you age.
Using Body Fat Percentage for Fitness Goals
Tracking body fat percentage provides a more meaningful measure of fitness progress than scale weight alone. During a well-designed training program, it is common to gain muscle while losing fat, resulting in minimal change on the scale despite significant improvements in body composition. By measuring body fat monthly, you can distinguish between productive recomposition (losing fat while gaining muscle) and unproductive weight changes. For fat loss goals, aim to reduce body fat by 1-2 percentage points per month through a moderate caloric deficit combined with resistance training. Our calorie calculator can help determine appropriate daily intake for your goals.
Common Mistakes to Avoid
- Measuring at inconsistent anatomical landmarks: Even small shifts in tape placement can change results by several percentage points. Always use bony landmarks as reference points and measure at the same locations each time.
- Pulling the tape too tight or too loose: The tape should contact the skin without indenting it. Consistent tension is critical for reliable tracking over time.
- Measuring at different times of day: Waist circumference can fluctuate by 1-2 cm throughout the day due to food, water intake, and bloating. Morning measurements before eating provide the most consistent results.
- Comparing results across different methods: Circumference estimates, bioelectrical impedance, DEXA, and calipers each produce different absolute values. Choose one method and use it consistently for tracking trends.
- Obsessing over single measurements: Body fat percentage fluctuates naturally. Focus on trends over 3-6 months rather than individual readings. A single high or low reading is not cause for alarm.
Frequently Asked Questions
The US Navy circumference method has been validated to estimate body fat within 3-4% of results from hydrostatic weighing for most individuals. It was developed by Hodgdon and Beckett at the Naval Health Research Center and is the standard method used by the US Department of Defense for fitness assessments. While less precise than laboratory methods like DEXA scanning or hydrostatic weighing, it provides a reliable estimate using only a tape measure. The method is most accurate for individuals with average body proportions and may be less accurate for highly muscular individuals or those with unusual fat distribution patterns. For clinical-grade accuracy, consult a healthcare professional who can perform more precise measurements.
Healthy body fat percentages differ significantly between males and females due to biological differences in essential fat requirements. For males, the American Council on Exercise defines the following categories: essential fat (2-5%), athlete (6-13%), fitness (14-17%), acceptable (18-24%), and obese (25% and above). For females, the categories are: essential fat (10-13%), athlete (14-20%), fitness (21-24%), acceptable (25-31%), and obese (32% and above). Women naturally carry more essential fat for reproductive and hormonal functions. The ideal percentage depends on your age, activity level, and health goals. Extremely low body fat can be as dangerous as very high body fat, potentially causing hormonal disruption, bone density loss, and immune dysfunction.
To measure your waist circumference accurately, stand upright with your feet shoulder-width apart and breathe normally. Locate the top of your hip bone (iliac crest) and the bottom of your rib cage. Place the tape measure horizontally around your abdomen at the midpoint between these two landmarks, which is typically at or near your navel. The tape should be snug against your skin but not compressing the tissue. Take the measurement at the end of a normal exhalation, not while holding your breath or sucking in your stomach. For the most consistent results, take three measurements and use the average. The US Navy method specifies measuring at the narrowest point of the abdomen for males and at the navel level for females.
The US Navy body fat formula uses different equations for males and females because fat distribution patterns differ between the sexes. Males typically store more fat in the abdominal region, so the male formula uses waist and neck circumferences along with height. Females tend to store more fat in the hips and thighs in addition to the abdomen, so the female formula adds hip circumference as a fourth measurement. These sex-specific formulas account for the biological differences in where fat is deposited and improve the accuracy of the body fat estimate for each group. Using the wrong formula can result in significantly inaccurate results.
Body fat percentage and BMI measure different things and can give conflicting assessments. BMI uses only height and weight to produce a simple ratio, while body fat percentage directly estimates the proportion of your weight that consists of fat tissue. A muscular individual may have a high BMI (overweight or obese category) but a healthy body fat percentage. Conversely, someone with low muscle mass could have a normal BMI but an elevated body fat percentage, a condition sometimes called skinny fat or metabolically obese normal weight. Body fat percentage provides a more accurate picture of body composition, but BMI is simpler to calculate and useful for population-level screening. Using both measurements together gives the most complete picture of body composition.
Yes, body fat percentage can be dangerously low. Essential fat is the minimum amount of fat required for basic physiological functions including hormone production, vitamin absorption, organ insulation, and temperature regulation. For males, essential fat is approximately 2-5%, and for females approximately 10-13%. Dropping below essential fat levels can cause serious health consequences including hormonal disruption (amenorrhea in women, testosterone reduction in men), weakened immune function, increased injury risk, chronic fatigue, impaired brain function, and cardiovascular complications. Athletes in sports that emphasize leanness such as bodybuilding, gymnastics, and distance running should be especially aware of these risks and work with sports medicine professionals to maintain safe body fat levels.
For general health monitoring, measuring body fat every 4-8 weeks is sufficient to track meaningful changes. Body fat does not change rapidly, and more frequent measurements can be misleading due to daily fluctuations in hydration, food intake, and measurement technique. For consistent results, always measure at the same time of day, under similar conditions (same state of hydration, same amount of clothing), and use the same measurement technique. If you are following a specific fitness or weight management program, monthly measurements can help track progress and guide adjustments. Recording your measurements in a log helps identify long-term trends rather than getting caught up in individual data points.
Several methods provide greater accuracy than circumference-based estimates. DEXA (Dual-Energy X-ray Absorptiometry) scanning is considered a gold standard, providing body fat accuracy within 1-2% along with detailed regional fat distribution data. Hydrostatic (underwater) weighing measures body density by comparing weight on land to weight underwater, with accuracy of 1-3%. Air displacement plethysmography (Bod Pod) measures body volume using air displacement and offers similar accuracy to hydrostatic weighing. Bioelectrical impedance analysis (BIA) sends a small electrical current through the body and estimates body fat based on the resistance encountered, though accuracy varies with hydration status. Skinfold calipers, when used by a trained professional at consistent sites, can achieve 3-4% accuracy. Each method has tradeoffs between accuracy, accessibility, and cost.
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Disclaimer: This calculator is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional for medical guidance.
Last updated: February 23, 2026
Sources
- Hodgdon & Beckett — US Navy Body Fat Formula: nhlbi.nih.gov/health/educational
- Centers for Disease Control and Prevention — Body Composition: cdc.gov/bmi/adult-calculator
- World Health Organization — Waist Circumference and Health: who.int/europe/news-room/fact-sheets