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Body Fat % Calculator

Estimate body fat percentage using the US Navy circumference method and BMI-based formula. ACE category classification, lean mass output. Metric and imperial.

Free · No sign-up · 6 languages
cm

Stand straight, measure from floor to top of head

cm

Measure just below the larynx, slightly downward slope

cm

Measure at the narrowest point (men: navel level)

kg

Optional — needed for fat mass & lean mass

💪

Enter your measurements above to see your body fat percentage

Worked Examples

Male: height 180 cm, neck 38 cm, waist 86 cm

BF% (Navy) = 495 / (1.0324 - 0.19077 x log10(86-38) + 0.15456 x log10(180)) - 450 = approximately 15.3%. ACE category: Fitness (14-17% for males). Lean mass = 80 kg x (1 - 0.153) = 67.8 kg. Target protein for muscle preservation: 67.8 x 1.8g = 122g/day.

Female: height 165 cm, neck 32 cm, waist 72 cm, hip 96 cm

BF% (Navy) = approximately 26.8%. ACE category: Acceptable (25-31% for females). Lean mass = 62 kg x (1 - 0.268) = 45.4 kg. A small reduction to 24% would move this into the Fitness category.

Athlete with overweight BMI: Male 85 kg, 175 cm

BMI = 85 / 1.75 squared = 27.8 — classified overweight. But neck 41 cm, waist 79 cm gives Navy BF% = 9.2%. ACE category: Athlete. This illustrates why BMI alone misclassifies muscular individuals — a lean, trained athlete is rated overweight by BMI but correctly assessed as having low body fat by the circumference method.

Frequently Asked Questions

5 min read
How accurate is the US Navy body fat method?▾
The US Navy circumference method has a published error margin of approximately 3-4% compared to DEXA (dual-energy X-ray absorptiometry) scan. This means a result of 20% body fat could represent a true value of 16-24%. The method is sufficient for tracking trends over time but not precise enough for clinical diagnosis. Consistent measurement technique — same time of day, same location, average of 3 readings — is critical for meaningful tracking.
What are the ACE body fat categories?▾
The American Council on Exercise (ACE) classifies body fat as follows. For males: Essential (2-5%), Athlete (6-13%), Fitness (14-17%), Acceptable (18-24%), Obese (25%+). For females: Essential (10-13%), Athlete (14-20%), Fitness (21-24%), Acceptable (25-31%), Obese (32%+). Women naturally carry more essential fat for hormonal and reproductive function.
How do I measure for the US Navy method?▾
Measure with a flexible tape at the same time each day (morning, before eating). For males: neck below the larynx angled slightly downward, abdomen at the navel level relaxed (not sucked in). For females: neck same as males, waist at the narrowest point between bottom rib and hip bone, hips at the widest point of the buttocks. Take each measurement three times and use the average.
What is lean mass and why does it matter?▾
Lean mass = weight x (1 - body fat fraction). For a 75 kg person at 20% body fat, lean mass = 75 x 0.80 = 60 kg. Lean mass includes muscle, bone, water, and organs. Protein requirements are based on lean mass — target 1.6-2.2g per kg lean mass to preserve muscle during a caloric deficit. A fitness goal should aim to reduce fat while preserving lean mass — total weight alone does not reveal whether you are losing fat or muscle.
Is body fat percentage more useful than BMI?▾
Body fat percentage is more diagnostically informative than BMI because it directly measures fat, not just total mass relative to height. BMI cannot distinguish between muscle and fat — a highly muscular person can have an overweight BMI with excellent body composition. However, circumference-based methods carry their own error margins and require careful technique.
What is a healthy body fat percentage for my age?▾
Healthy body fat increases slightly with age. For males aged 20-39, the fitness category is 8-19%; for 40-59, it is 11-21%; for 60+, it is 13-24%. For females aged 20-39, fitness is 21-32%; for 40-59, 23-33%; for 60+, 24-35%. Some increase in adiposity with age is physiologically normal.
Can I use this calculator if I am very tall or very short?▾
The US Navy formula is validated for heights approximately 150-200 cm. At extreme heights outside this range, the logarithmic relationships become less reliable. For heights outside the normal range, a BMI-based body fat estimate or a direct measurement method (calipers or DEXA) is more appropriate.
How quickly can body fat percentage change?▾
Losing 0.5-1% body fat per month is a sustainable rate that minimises muscle loss. At a deficit of 500 kcal/day, an 80 kg person at 20% body fat loses approximately 2 kg/month — mostly fat if protein intake is adequate. More aggressive deficits accelerate muscle loss alongside fat, resulting in worse body composition even if the scale drops faster.

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Body fat estimates from circumference measurements carry approximately 3-4% error compared to DEXA scan. Results are for personal tracking, not clinical diagnosis. Consult a healthcare professional for body composition assessment.

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