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Body Fat Calculator

Estimate your body fat percentage with the U.S. Navy tape-measure method, plus fat mass, lean mass, and your ACE category

By Waqar Mushtaq · Last updated:

US (lb, in)
Male

Body fat percentage is the share of your total weight that is fat. It says more about health and fitness than weight or BMI alone, because two people with the same weight and height can carry very different amounts of fat and muscle. This calculator estimates it with the U.S. Navy method -- a tape-measure formula from height and neck and waist (plus hip, for women) circumferences -- and shows your fat mass, lean mass, and where you sit on the American Council on Exercise (ACE) body fat scale. It also gives the BMI-based estimate (Deurenberg equation) side by side, so you can see how far a height-and-weight guess is from a measurement, and a table of what you'd weigh at other body fat levels with the same lean mass. Metric, US, and UK units are supported.

How Body Fat Is Calculated

O(1) calculation
%BFmen=86.010log⁡10(waist−neck)−70.041log⁡10(height)+36.76\%BF_{\text{men}} = 86.010 \log_{10}(\text{waist} - \text{neck}) - 70.041 \log_{10}(\text{height}) + 36.76

U.S. Navy method, men -- all measurements in inches

%BFwomen=163.205log⁡10(waist+hip−neck)−97.684log⁡10(height)−78.387\%BF_{\text{women}} = 163.205 \log_{10}(\text{waist} + \text{hip} - \text{neck}) - 97.684 \log_{10}(\text{height}) - 78.387

U.S. Navy method, women -- all measurements in inches

%BFBMI=1.20×BMI+0.23×age−10.8×sex−5.4\%BF_{\text{BMI}} = 1.20 \times \text{BMI} + 0.23 \times \text{age} - 10.8 \times \text{sex} - 5.4

Deurenberg BMI method for adults · sex = 1 for men, 0 for women

The U.S. Navy equations were developed by Hodgdon and Beckett at the Naval Health Research Center in 1984, fitted against underwater weighing, and later adopted Department of Defense-wide; the Army still uses them for its tape test. They're defined in inches -- metric measurements are converted before applying them. (A metric version using 495 / density − 450 also circulates; it comes from a different fit and gives slightly different results.)

Example -- man: height 70 in, neck 15 in, waist 34 in. 86.010 × log₁₀(34 − 15) − 70.041 × log₁₀(70) + 36.76 = 86.010 × 1.2788 − 70.041 × 1.8451 + 36.76 ≈ 17.5% body fat. At 80 kg (176 lb), that's 14 kg of fat and 66 kg of lean mass.

Fat mass and lean mass:

  • Fat mass = weight × body fat %
  • Lean mass = weight − fat mass

Weight at another body fat level assumes lean mass stays the same: weight = lean mass / (1 − target body fat). For the example above, reaching 13% means 66 / 0.87 = 75.9 kg.

How to measure: measure the neck just below the larynx, sloping slightly down to the front. Men measure the waist horizontally at the navel; women measure at the narrowest point of the waist and around the widest part of the hips. Keep the tape snug but not compressing the skin, don't suck in, and take each measurement two or three times.

ACE categories: the American Council on Exercise groups results as essential fat (men 2–5%, women 10–13%), athletes (6–13% / 14–20%), fitness (14–17% / 21–24%), average (18–24% / 25–31%), and obese (25%+ / 32%+).

Use Cases

Tracking Fitness Progress

Weight can stay flat while you lose fat and gain muscle. Re-measuring every few weeks with the same tape and technique shows the change in body fat that a scale can't.

Setting a Realistic Weight Goal

The "other body fat levels" table turns a body fat target into a weight target, based on your current lean mass -- a more grounded goal than an arbitrary number on the scale.

Checking a BMI Result

BMI flags many muscular people as overweight. Comparing the tape-measure estimate with the BMI-based one shows whether your BMI is driven by fat or by muscle.

Military Body Composition Standards

The Navy equations are the basis of U.S. military tape tests. For the Army's own age-based limits, see the Army Body Fat Calculator.

Frequently Asked Questions

How accurate is the U.S. Navy body fat method?

In the original validation it agreed with underwater weighing to within about 3 percentage points for most people, which is good for a tape measure. It tends to underestimate body fat at the high end and overestimate it in very lean people, and careless measuring adds more error than the formula. For a precise number, DEXA or hydrostatic weighing is more accurate; for tracking change over time, consistent tape measurements work well.

What is a healthy body fat percentage?

The ACE ranges are a common guide: about 14–24% for men and 21–31% for women covers the fitness and average categories. Going below essential fat (about 2–5% for men, 10–13% for women) is unhealthy, and the obese range starts at 25% for men and 32% for women. Healthy body fat also rises somewhat with age.

Why do women have a higher body fat percentage than men?

Women carry more essential fat -- in the breasts, hips, and thighs -- that supports hormonal and reproductive function. That's why every ACE category sits about 7–8 percentage points higher for women, and why the Navy formula for women adds a hip measurement.

Why does the BMI method give a different answer?

The Deurenberg equation estimates body fat from BMI, age, and sex alone, so it assumes average muscle mass for your size. If you're more muscular than average it overestimates your body fat; if you have less muscle it underestimates. The tape-measure method responds to where your fat actually is, so it's usually the better of the two.

Is this calculator suitable for children?

No -- both equations were fitted on adults, so this calculator requires an age of 18 or over. Children's body fat is usually assessed with BMI-for-age percentiles instead.

How do I lose body fat without losing muscle?

A moderate calorie deficit, enough protein, and regular strength training help preserve lean mass while losing fat. The weight targets in this calculator assume all of the loss is fat, so they're the best case -- losing some muscle along the way means you'd need to weigh a little less to hit the same body fat percentage.

Methodology

The formula above is implemented as a standalone module covered by unit tests, so its worked examples are re-checked on every change to the site. It is verified against the authoritative sources listed below.

Not medical advice. This calculator is a general informational tool and cannot account for your individual circumstances. See the terms of use.

Maintained by Waqar Mushtaq. Spotted a result that looks wrong? Report it and it becomes a failing test.

Sources

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