Body Fat Calculator

The Body Fat Calculator estimates your body fat percentage using the U.S. Navy circumference method — the same tape-measure equations long used for military fitness standards. Choose a gender tab and a unit preference, then enter three measurements for men (height, neck, and waist) or four for women (adding hip), and the tool applies the Navy formula: 495 divided by a logarithmic expression built from those measurements, minus 450. The result appears as a percentage with a category badge drawn from American Council on Exercise ranges, spanning Essential, Athletic, Fitness, Average, and Obese. Because the formula involves logarithms of measurement differences, the calculator validates its inputs carefully — if your waist is not greater than your neck, or waist plus hip not greater than neck, it shows a clear error instead of a nonsense number and surfaces the same message as a toast notification. The cm/in toggle converts inches internally, so imperial users get the same precision as metric ones. Fitness enthusiasts, bodybuilders, and anyone tracking recomposition use it as a repeatable, tape-measure-based body fat percentage estimate that complements scale weight — with the honest caveat printed on the page that clinical body composition assessment requires a healthcare professional.

1. 1

   Pick the Male or Female tab — the female tab adds a required Hip field and uses a different formula.

2. 2

   Choose cm or in with the unit toggle beside the gender tabs.

3. 3

   Enter Height, Neck, and Waist (plus Hip for female), measured with a flexible tape.

4. 4

   Read the large body fat percentage and its ACE category badge, colour-coded by band.

5. 5

   If an error appears — such as waist not greater than neck — correct the measurements and the result returns.

• Tracking recomposition progress with a tape measure between weigh-ins.
• Estimating body composition for a fitness assessment alongside the BMI tool.
• Checking against military or academy fitness standard expectations.
• Setting a body fat target before starting a cut or bulk.
• Comparing readings from month to month under the same measuring routine.
• Giving a coach a starting baseline before a training block.

• Measure the neck below the larynx and the waist at the navel, exactly as the Navy method specifies.
• Keep conditions consistent — same time of day, same posture, same tape tension — or trends become noise.
• Fix invalid geometry before reading results: waist must exceed neck for men, and waist plus hip must exceed neck for women.
• Treat the output as an estimate, not a clinical measurement — the page itself recommends professionals for clinical body composition.
• Have the same person take the measurements each time to reduce inter-rater error.
• Pair the percentage with scale weight and photos, since the formula only sees circumferences.

• Switch units freely — the toggle only changes the input fields, never the underlying formula.
• Use the same tape routine each time; the tool's precision is only as good as your measurements.
• Read the inline error text carefully — it tells you exactly which measurement pair is invalid.
• Compare the badge to the ACE chart on the page to judge where you sit within your band.