What body fat percentage tells you that weight cannot
Two people can weigh exactly the same and look, feel and function very differently, because weight mixes together fat, muscle, bone, organs and water. Body fat percentage separates one part of that mix: the share of your weight that is fat tissue. Some fat is essential. It protects organs, stores energy, makes hormones and keeps you warm. Too little is a health problem, and a great deal extra is linked with higher average risk of several conditions, so the useful question is not how low the number can go but whether it sits in a reasonable range for you.
This page uses the circumference method developed for the U.S. Navy, which estimates body fat from a few tape measurements and height. It was designed to screen large numbers of people quickly without special equipment. It is not as precise as a DEXA scan or hydrostatic weighing, and its error can be several percentage points, but for tracking your own trend with the same tape and the same technique it is practical and honest. This calculator is for information only and is not medical advice.
The U.S. Navy formulas
Measurements are in centimetres. For women the formula is BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387, because fat distribution differs and the hip measurement adds important information. The logic is intuitive: for the same height, a larger waist relative to the neck points to more stored fat.
How to measure well
Use a flexible tape, stand relaxed, and do not pull the tape tight enough to press into the skin. Measure the neck just below the Adam's apple, the waist at the navel for men and at the narrowest point for women, and the hip at the widest point. Measure twice and use the average. The hip field is only used for women, which is why it is labelled that way, but it stays visible so you can see the full method. Fat mass is your weight multiplied by the percentage; lean mass is everything that remains.
Worked example
A man, 175 cm and 70 kg, with a 38 cm neck and an 85 cm waist: waist − neck = 47. BF% = 86.010 × log10(47) − 70.041 × log10(175) + 36.76 = about 23.5%. Fat mass is 0.235 × 70 = about 16.4 kg, and lean mass is about 53.6 kg.
How to use this calculator
- Choose units and select your sex.
- Enter your weight and height.
- Measure neck, waist and, for women, hip with a flexible tape as described.
- Read your estimated body fat percentage, fat mass and lean mass.
- Compare your result with the category table for both sexes below.
Categories, limits and healthy context
The category ranges in the table are the widely used American Council on Exercise ranges. Women naturally carry a higher essential fat percentage than men, which is why the two rows differ so much; comparing across sexes is meaningless. Athletes in lean sports often sit in the athletes range, while many healthy, active adults sit comfortably in the fitness or average ranges.
Chasing the lowest possible number is not a health goal. Very low body fat can disrupt hormones, mood, immunity and, for women, the menstrual cycle. Equally, a single estimate should never be used to judge yourself harshly: tape placement, time of day and recent meals all move the result. Track the direction over months, combine it with how you feel and perform, and talk to a qualified professional about any real concern. For information only, not medical advice.
Important note
For information only — not medical advice. This calculator uses standard published formulas to estimate values for general education and planning. It does not diagnose, treat, or replace the advice of a doctor or other qualified health professional. If you have a health concern, are pregnant, or are making decisions about treatment, medication, or a major diet or exercise change, please talk to a healthcare professional first.