For educational purposes only. Not personalised health advice. This calculator has not been reviewed by a registered dietitian, physician or exercise physiologist. Results are population estimates and can be wrong for you individually. Speak to a qualified professional before acting on them, particularly if you are pregnant, under 18, managing a medical condition, or have a history of disordered eating.
Body Fat Calculator
Body fat percentage tells you far more about body composition than weight alone, and this calculator estimates it using the US Navy circumference method, a tape-measure approach that needs no special equipment. For men it combines the waist, neck and height; this version uses the male formula, so enter those three measurements in inches and the tool returns an estimated body fat percentage. The method works by relating the girths of the body to the proportion of fat tissue through a logarithmic relationship, which is why a larger waist relative to neck pushes the estimate up. Its great strength is convenience and repeatability: with a flexible tape you can track changes over weeks and months at almost no cost. It is less precise than laboratory methods such as DEXA or hydrostatic weighing, and it can read high or low for very muscular or very lean builds, so it is best used as a trend indicator rather than an exact clinical figure. Take each measurement snug but not tight, breathe normally, and average a few readings for consistency. Because everyone's measurements differ, all inputs are fully editable. The exact formula is shown below, with a worked example that reconciles exactly to the calculator defaults.
The US Navy method estimates fat from tape girths: body fat % = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76. A 34 in waist, 16 in neck and 70 in height give about 15.49% body fat.
Body fat formula (US Navy, men)
BF% = 86.010 x log10(W - N) - 70.041 x log10(H) + 36.76
W = waist circumference in inches
N = neck circumference in inches
H = height in inches
log10 is the base-10 logarithm
The difference between waist and neck captures abdominal girth, and dividing its effect against height through logarithms scales it into a body fat percentage estimate.
Worked example
A man measures a 34 inch waist, a 16 inch neck and a 70 inch height.
- Waist minus neck = 34 - 16 = 18; log10(18) = 1.255273
- log10(70) = 1.845098
- 86.010 x 1.255273 = 107.965
- 70.041 x 1.845098 = 129.243
- BF% = 107.965 - 129.243 + 36.76 = 15.49%
The estimated body fat is about 15.49%. These are the calculator's default inputs, so the result above matches the widget exactly.
Body fat versus BMI, and how much to trust the number
Body-fat percentage answers the question BMI cannot: how much of you is fat rather than muscle, bone and water. That is why a lean, muscular person can be flagged 'overweight' by BMI yet sit at a healthy body-fat level, and why the two metrics are companions rather than rivals.
What matters is the method behind the estimate. A tape-based approach such as the US Navy formula is free and repeatable but carries an error of several percentage points. Skinfold calipers are more precise in trained hands and unreliable in untrained ones. Bioelectrical scales swing with hydration, so a morning and evening reading can differ by points. Laboratory methods, DEXA and hydrostatic weighing, are the reference standards but cost money and access. Whatever you use, the trend across weeks measured the same way, same time of day, same conditions, is far more meaningful than any single figure.
Use sensible reference bands rather than chasing a low number: essential fat is roughly 3 to 5 percent for men and 10 to 13 percent for women, and going near those floors is neither healthy nor sustainable for most people. A 'good' range is one you can hold without harming performance, hormones or sleep.
Body fat calculator: frequently asked questions
How does the US Navy body fat method work?
It estimates body fat percentage from simple tape measurements rather than calipers or scales. For men it uses waist, neck and height; for women it adds the hip measurement. The measurements are combined in a logarithmic formula. For a man with a 34 inch waist, 16 inch neck and 70 inch height, the result is about 15.5% body fat.
How do I take the measurements correctly?
Measure with a flexible tape, snug but not compressing the skin. For men, measure the waist at the navel and the neck just below the larynx. Stand relaxed and breathe normally rather than sucking in. Take each measurement two or three times and average them, since small differences in tape placement noticeably change the result.
How accurate is this estimate?
The circumference method is a quick, low-cost estimate that works well for tracking change over time, but it is less precise than methods like DEXA or hydrostatic weighing. It can be off for very muscular or very lean builds because it infers fat from girths. Treat the number as a useful trend indicator rather than an exact clinical measurement.
What is a healthy body fat percentage?
Healthy ranges vary by age and sex and are best interpreted with a health professional. As a general guide, essential fat is higher for women than men, and athletic ranges sit below typical fitness ranges. Rather than fixating on a single target, watch the trend and pair it with other measures of health and fitness.
What is the US Navy body fat formula for men?
Body fat % = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76, with all measurements in inches. For a 34 inch waist, 16 inch neck and 70 inch height, that is 86.010 x log10(18) - 70.041 x log10(70) + 36.76, which is about 15.49%.
Official sources
- Measurement standards and units: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
This content is provided for educational purposes only and has not been reviewed by a qualified specialist in this field. See our methodology. This is general information, not financial, tax, legal, investment or medical advice.