Body Fat Calculator
Estimate your body fat percentage using the US Navy method. Requires height, weight, waist, and neck measurements. See also BMI Calculator and Ideal Weight Calculator.
How to Calculate Body Fat Percentage
The US Navy body fat formula estimates body fat percentage using circumference measurements. For men, it uses waist and neck measurements. For women, it adds hip measurement. The formula uses logarithmic calculations based on the relationship between body circumferences and body density. While not as accurate as DEXA scans or hydrostatic weighing, it provides a reasonable estimate using only a tape measure.
US Navy Body Fat Formula
For Men:
For Women:
Body Fat Categories
| 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%+ |
Frequently Asked Questions
How accurate is the US Navy body fat method?
The US Navy method is accurate to within 1-3% for most people when measurements are taken correctly. It is less accurate for very lean or very obese individuals. For clinical accuracy, DEXA scans or hydrostatic weighing are preferred.
Where should I measure my waist?
Measure at the narrowest point of your waist, typically at the navel level. For the Navy method specifically, measure at the navel for men. Stand relaxed and don't suck in your stomach.
What is a healthy body fat percentage?
For men, 14-17% is considered fit, and 18-24% is average. For women, 21-24% is fit, and 25-31% is average. Essential fat (minimum for health) is 2-5% for men and 10-13% for women.
Solved Examples
Example 1: Body Fat for a Male (Height 180 cm, Waist 90 cm, Neck 38 cm)
Solution:
Step 1: Waist − Neck = 90 − 38 = 52 cm
Step 2: log10(52) = 1.7160
Step 3: log10(180) = 2.2553
Step 4: BF% = 495 / (1.0324 − 0.19077 × 1.7160 + 0.15456 × 2.2553) − 450
Step 5: = 495 / (1.0324 − 0.3274 + 0.3486) − 450 = 495 / 1.0536 − 450 = 19.8%
Answer: Body fat = 19.8% (Average category for males)
Example 2: Body Fat for a Female (Height 165 cm, Waist 75 cm, Hip 98 cm, Neck 32 cm)
Solution:
Step 1: Waist + Hip − Neck = 75 + 98 − 32 = 141 cm
Step 2: log10(141) = 2.1492
Step 3: log10(165) = 2.2175
Step 4: BF% = 495 / (1.29579 − 0.35004 × 2.1492 + 0.22100 × 2.2175) − 450
Step 5: = 495 / (1.29579 − 0.7523 + 0.4901) − 450 = 495 / 1.0336 − 450 = 28.9%
Answer: Body fat = 28.9% (Average category for females)
Example 3: Calculate Lean Mass and Fat Mass (Male, 85 kg, 22% body fat)
Solution:
Step 1: Fat mass = Total weight × (body fat% / 100)
Step 2: Fat mass = 85 × 0.22 = 18.7 kg
Step 3: Lean mass = Total weight − Fat mass = 85 − 18.7 = 66.3 kg
Step 4: Lean mass includes muscle, bone, organs, and water
Answer: Fat mass = 18.7 kg, Lean mass = 66.3 kg
Practice Questions
Q1: A male has waist 85 cm and neck 40 cm at height 175 cm. Estimate his body fat category.
Answer: Waist−Neck = 45. BF% ≈ 495/(1.0324 − 0.19077×log10(45) + 0.15456×log10(175)) − 450 ≈ 17.2% (Fitness category).
Q2: A woman weighs 70 kg with 30% body fat. How much fat would she need to lose to reach 22% body fat (assuming lean mass stays the same)?
Answer: Current fat = 70 × 0.30 = 21 kg. Lean mass = 49 kg. At 22%: 49 / 0.78 = 62.8 kg total. Fat needed = 62.8 − 49 = 13.8 kg. Lose: 21 − 13.8 = 7.2 kg of fat.
Q3: Two men both weigh 90 kg at 180 cm. One has 15% body fat, the other 28%. What is their lean mass difference?
Answer: Man 1: lean = 90 × 0.85 = 76.5 kg. Man 2: lean = 90 × 0.72 = 64.8 kg. Difference = 11.7 kg more lean mass.
Q4: Is a male with 5% body fat healthy?
Answer: No — 2-5% is essential fat territory for males. Below 6% is dangerous for long-term health. This level is only seen temporarily in competition bodybuilders and is not sustainable.
Q5: A male's waist measures 95 cm in the morning and 99 cm in the evening. Which should he use?
Answer: Always measure in the morning, before eating, at the same time for consistency. The morning measurement (95 cm) is the standard. Evening bloating from food and water adds 2-5 cm and gives artificially high body fat readings.
Common Mistakes to Avoid
The most critical mistake with the Navy body fat method is measuring at the wrong anatomical points — waist should be measured at the navel level (not the narrowest point), and neck should be measured just below the larynx. Measuring too high or low on the waist can swing results by 2-5%. Another common error is measuring at inconsistent times of day: after eating, the waist can expand 2-5 cm from food and water, giving artificially high readings. Always measure first thing in the morning on an empty stomach. People also make the mistake of sucking in their stomach during measurement — stand relaxed with normal posture. For females, forgetting to include the hip measurement (or measuring it at the wrong point — it should be at the widest part of the buttocks) invalidates the entire calculation. Finally, many users expect day-to-day precision from this method, but natural fluctuations of 1-2% are normal due to hydration, food intake, and hormonal changes.
Key Takeaways
- The US Navy method estimates body fat within 1-3% accuracy when measurements are taken correctly and consistently.
- Males use waist and neck measurements; females also require hip measurement for an accurate calculation.
- Healthy body fat ranges differ by gender: 14-17% (fitness) for men, 21-24% (fitness) for women.
- Always measure in the morning, standing relaxed, at the same time of day for consistent tracking over time.
- Body fat percentage is more meaningful than BMI for assessing body composition — two people at the same BMI can have very different body fat levels.
- Essential fat (2-5% men, 10-13% women) is the minimum required for basic physiological functions — going below is dangerous.