Body Fat Percentage Calculator
Compute body fat percentage using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Formula
BF% (Male) = 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450
The U.S. Navy method calculates body fat percentage using circumference measurements in centimeters. For males: uses height, waist, and neck. For females: uses height, waist, neck, and hip. The formula derives body density from the ratio of these measurements using logarithmic equations, then converts density to body fat percentage. Fat mass = weight x BF%, Lean mass = weight - fat mass.
Worked Examples
Example 1: Male Body Fat Estimation
Problem: Male, 5'10\" (70 inches), waist 34 inches, neck 15 inches, weight 180 lbs.
Solution: Convert to cm: Height = 177.8 cm, Waist = 86.4 cm, Neck = 38.1 cm\nNavy formula (male): 495 / (1.0324 - 0.19077 x log10(86.4 - 38.1) + 0.15456 x log10(177.8)) - 450\n= 495 / (1.0324 - 0.19077 x 1.684 + 0.15456 x 2.250) - 450\n= 495 / (1.0324 - 0.3213 + 0.3478) - 450\n= 495 / 1.0589 - 450 = 17.5%\nFat mass: 180 x 0.175 = 31.5 lbs\nLean mass: 180 - 31.5 = 148.5 lbs
Result: Body Fat: 17.5% | Fat Mass: 31.5 lbs | Lean Mass: 148.5 lbs | Category: Fitness
Example 2: Female Body Fat Estimation
Problem: Female, 5'5\" (65 inches), waist 30 inches, neck 13 inches, hip 38 inches, weight 140 lbs.
Solution: Convert to cm: Height = 165.1 cm, Waist = 76.2 cm, Neck = 33.0 cm, Hip = 96.5 cm\nNavy formula (female): 495 / (1.29579 - 0.35004 x log10(76.2 + 96.5 - 33.0) + 0.22100 x log10(165.1)) - 450\n= 495 / (1.29579 - 0.35004 x 2.145 + 0.22100 x 2.218) - 450\n= 495 / (1.29579 - 0.7508 + 0.4902) - 450\n= 495 / 1.0352 - 450 = 28.2%\nFat mass: 140 x 0.282 = 39.5 lbs\nLean mass: 140 - 39.5 = 100.5 lbs
Result: Body Fat: 28.2% | Fat Mass: 39.5 lbs | Lean Mass: 100.5 lbs | Category: Average
Frequently Asked Questions
What is the Navy Method for body fat calculation?
The U.S. Navy body fat estimation method uses circumference measurements to calculate body fat percentage without expensive equipment like DEXA scans or hydrostatic weighing. For men, it requires height, waist circumference (at the navel), and neck circumference. For women, it additionally requires hip circumference at the widest point. The formula uses logarithmic calculations based on the relationship between these body measurements and body density. Studies show the Navy method is accurate within 1-3% compared to hydrostatic weighing for most individuals. It is widely used by the U.S. military for fitness assessments and body composition standards.
What is a healthy body fat percentage?
Healthy body fat ranges differ significantly between men and women due to biological differences. For men, essential fat is 2-5%, athletic is 6-13%, fitness is 14-17%, average is 18-24%, and above 25% is considered obese. For women, essential fat is 10-13%, athletic is 14-20%, fitness is 21-24%, average is 25-31%, and above 32% is obese. Women naturally carry more essential fat for reproductive function and hormone production. Athletes may function well at lower percentages, but dropping below essential fat levels causes hormonal disruption, weakened immunity, and bone density loss. Most health professionals recommend targeting the fitness range for optimal health and longevity.
What is the difference between fat mass and lean mass?
Fat mass refers to all body fat including essential fat (around organs, bone marrow, nervous system) and storage fat (subcutaneous and visceral). Lean mass, also called fat-free mass, includes everything else: muscle, bone, water, organs, and connective tissue. Lean mass is metabolically active, meaning it burns calories at rest, while fat mass is relatively metabolically inert. When losing weight, the goal should be maximizing fat mass loss while preserving lean mass. This is achieved through adequate protein intake (0.7-1.0g per pound), resistance training, moderate caloric deficit (500 calories or less), and sufficient sleep. Crash diets and excessive cardio without resistance training tend to cause disproportionate lean mass loss.
How can I reduce my body fat percentage?
Reducing body fat percentage requires a sustained caloric deficit combined with strategies to preserve lean muscle mass. Start with a moderate deficit of 300-500 calories below your TDEE, prioritize protein intake at 1.0 grams per pound of body weight, and follow a progressive resistance training program 3-4 times per week. Cardiovascular exercise helps create additional deficit but should complement, not replace, strength training. Sleep 7-9 hours per night, as poor sleep increases cortisol and promotes fat storage. Manage stress through mindfulness or other techniques, as chronic stress elevates cortisol. Expect to lose 0.5-1% body fat per month with consistent effort. Rapid fat loss attempts often result in muscle loss and metabolic adaptation.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
What formula does Body Fat Percentage Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.