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Body Fat Calculator

Free body fat calculator using the U.S. Navy circumference method. Estimate body fat percentage, fat mass, lean mass and ideal target by age - metric or imperial.

years
cmftin
kg
cm
cm
cm
Result
Body Fat (U.S. Navy Method)24.1%
Body Fat CategoryFitness
Body Fat Mass16.9 kg
Lean Body Mass53.1 kg
Ideal Body Fat for Given Age
(Jackson & Pollock)		18.4%
Body Fat to Lose to Reach Ideal4.0 kg
Body Fat (BMI method)26.9%

Body Fat Categories

According to the American Council on Exercise (ACE)

Male

CategoryBody Fat Range
Essential Fat2-5%
Athletes6-13%
Fitness14-17%
Average18-24%
Obese25%+

Female

CategoryBody Fat Range
Essential Fat10-13%
Athletes14-20%
Fitness21-24%
Average25-31%
Obese32%+

Ideal Body Fat Percentages by Age (Jackson & Pollock)

AgeFemaleMale
2017.7%8.5%
2518.4%10.5%
3019.3%12.7%
3521.5%13.7%
4022.2%15.3%
4522.9%16.4%
5025.2%18.9%
5526.3%20.9%

What is body fat percentage?

Body fat percentage is the share of your total body weight made up of fat tissue. It includes essential fat (needed for organ function, hormones and reproduction) and storage fat (the fat under your skin and around your organs). Body fat percentage is generally a more useful health indicator than BMI because it separates fat tissue from lean mass, so a heavy athlete and a sedentary person of the same BMI can have very different health risk profiles.

U.S. Navy method

The U.S. Navy circumference method uses height plus neck and waist (and hip for women) to estimate body fat percentage. Developed by the Naval Health Research Center (Hodgdon and Beckett, 1984), it correlates within about 3-4 percentage points of hydrostatic weighing for most adults, making it the most accurate method you can do at home with just a tape measure. The price is sensitivity to measurement technique - a 2 cm error on the waist can shift the result by 1-2 points.

Formulas

Male:

Body Fat % = 86.010 × log10(waist - neck) - 70.041 × log10(height) + 36.76

Note: Measurements are converted from cm to inches for calculation

Female:

Body Fat % = 163.205 × log10(waist + hip - neck) - 97.684 × log10(height) - 78.387

Note: Measurements are converted from cm to inches for calculation

Essential vs. storage body fat

Essential body fat is the fat your body genuinely needs to function: it lines organs, supports hormone production and protects nerves. The minimum survivable level is about 2-5% for men and 10-13% for women - women carry more essential fat for reproductive function. Going below those minimums is dangerous regardless of how lean you look.

Storage fat is the rest: subcutaneous (under the skin) and visceral (around organs). Some storage fat is healthy - it cushions organs, insulates against cold and stores energy. Excessive storage fat, especially visceral fat, is what raises cardiovascular and metabolic risk.

Health considerations

A healthy body fat percentage supports hormones, immune function, bone density, mood and athletic performance. Both extremes - too high and too low - cause real medical problems, which is why category guidance exists.

Excess body fat, particularly visceral fat around the organs, is linked to type 2 diabetes, hypertension, heart disease, stroke, several cancers, fatty liver disease, obstructive sleep apnoea and osteoarthritis. Waist circumference and waist-to-height ratio are stronger predictors of these risks than total body fat percentage alone.

Very low body fat is also dangerous. Below 5% in men and 13% in women, you can develop hormonal collapse, suppressed immunity, reduced bone density, fertility problems, heart rhythm issues and severe fatigue. Athletes and physique competitors who hit very low percentages should do so only briefly and under medical supervision.

Frequently Asked Questions

For at-home estimation, the U.S. Navy circumference method (used by this calculator) is the most accurate widely-available option, sitting within about 3-4 percentage points of gold-standard hydrostatic weighing. Skinfold calipers are similar in accuracy but require practice and a partner. Bioelectrical impedance (BIA) bathroom scales are convenient but vary by ±5-10 points depending on hydration. DEXA scans are the medical gold standard, accurate within 1 point, but cost money and require a clinic visit. The honest ranking for free home use: U.S. Navy with carefully taken measurements > calipers > BIA.

Multiple validation studies show U.S. Navy results correlate with DEXA at r ≈ 0.88-0.92 for both sexes, and the average error is 3-4 percentage points. The formula systematically underestimates body fat in very lean athletic men (because it cannot separate dense muscle from lean tissue) and overestimates in older sedentary women (because waist circumference is influenced by abdominal posture and bowel content). For monitoring changes over weeks and months, it is reliable; for a single absolute reading you can quote to your doctor, prefer DEXA.

The 1984 Hodgdon-Beckett study found that for men, neck and waist plus height were the best three predictors of underwater-weighed body fat. Adding hip improved the female formula because women carry more gluteal-femoral fat, so the hip measurement captures variance that neck and waist miss. For men, adding hip actually slightly worsened the predictions in the original derivation. The formula trusts the data: if a measurement was not predictive enough to justify the extra friction, it was dropped.

The Navy protocol measures waist at the narrowest point above the navel, parallel to the floor, at the end of a normal exhale. Stand naturally - no sucking in, no pushing out. Use a non-stretch tape pulled snug to the skin but not compressing it. Measure twice and use the average; if your two readings differ by more than 1 cm, take a third. Common mistakes that inflate the reading: measuring after a heavy meal, holding the breath in, measuring over clothing, taking the widest belly point instead of the narrowest waist.

Body fat percentage matters more in this conflict. BMI cannot separate muscle from fat, so a muscular athlete or a regular lifter often shows obese on BMI while sitting at 15% body fat. The DEXA-validated rule of thumb: when BMI and body fat disagree, trust waist circumference plus body fat. If your waist-to-height ratio is below 0.5 and body fat is in the healthy range, BMI is mislabelling you. The reverse - BMI normal but body fat high - is called "normal-weight obesity" and is associated with higher cardiometabolic risk than the BMI alone suggests.

About 0.5 to 1 percentage point per month for most people, which corresponds roughly to 0.5-1 kg of fat lost per week from a 300-500 kcal daily deficit while keeping protein at 1.6-2.2 g/kg of body weight. Going faster requires deeper deficits that increase muscle loss and slow metabolic adaptation. The best practical signal: if the scale is dropping but your tape measurements (waist, hip) are not, you are probably losing muscle and water, not fat. Slow down, eat more protein and keep lifting.

The American Council on Exercise (ACE) categories are descriptive, not prescriptive. "Fitness" range (14-17% men, 21-24% women) is a sensible long-term target for most active adults and is associated with the lowest all-cause mortality in large studies. "Athletes" range (6-13% men, 14-20% women) is sustainable for serious competitors but is not where most people should live year-round, especially women, where below 18-20% can disrupt menstrual cycles. "Average" (18-24% men, 25-31% women) is the population norm and is not unhealthy if waist circumference and metabolic markers are good.

It uses the Jackson & Pollock ideal-by-age table, which acknowledges that some increase in body fat with age is normal and not harmful. After about age 25, men gain roughly 0.5-1 kg of fat per decade if weight is otherwise stable, and women gain 1-1.5 kg per decade with steeper jumps around perimenopause. Trying to hit the 25-year-old target at 50 means fighting both physiology and hormones - it is achievable but requires aggressive training and a strict diet. The age-adjusted ideal is a reasonable practical target most people can sustain without making fitness their entire identity.
Body Fat Calculator — Free body fat calculator using the U.S. Navy circumference method. Estimate body fat percentage, fat mass, lean mass and
Body Fat Calculator
See also
Health & FitnessHEALTH & FITNESS32
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