Body Fat Calculator

What is body fat percentage?

A body fat calculator estimates what share of your total weight is fat tissue rather than muscle, bone and water. Two people can weigh exactly the same and look completely different — the difference is body composition. That is why body fat percentage is a better fitness indicator than the scale alone, and why athletes track it instead of just weight.

This calculator uses the U.S. Navy method, developed for the American armed forces as a field test that needs nothing more than a tape measure. It estimates body fat from a few circumference measurements plus your height, using logarithmic formulas validated against laboratory methods.

How it works

Men: body fat % = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76

Women: body fat % = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

All measurements are in centimetres. The logic is straightforward: a waist much larger than the neck suggests more abdominal fat, while height puts the numbers in proportion. Women include a hip measurement because fat distributes differently.

Measuring tips

• Neck: just below the Adam's apple, tape snug but not tight.
• Waist: at the navel, relaxed — do not suck in your stomach.
• Hip (women): at the widest point.
• Measure in the morning before eating, and use the same spot each time.

How to use this calculator

1. Select your gender.
2. Enter height, neck and waist (plus hip for women), all in centimetres.
3. Read your estimated body fat percentage.

Worked example

A man, height 175 cm, neck 38 cm, waist 85 cm:

Body fat % = 86.010 × log₁₀(85 − 38) − 70.041 × log₁₀(175) + 36.76
= 86.010 × 1.6721 − 70.041 × 2.2430 + 36.76
= 23.5%

Rough healthy ranges are about 10–20% for men and 18–28% for women, varying with age — so 23.5% suggests room for improvement through training and diet.

Limitations and tips

• Good for trends, not lab precision: the Navy method usually lands within a few percentage points of the true value — fine for tracking progress, less exact than a DEXA scan.
• Tape technique matters: a centimetre of error at the waist moves the result noticeably. Measure carefully and consistently.
• Very lean or very heavy bodies: the formula is least accurate at the extremes; treat unusual results with caution.
• Track monthly: body composition changes slowly. Measure once a month under the same conditions and watch the trend, not daily noise.