About the Body Fat Calculator
Estimate body fat percentage with nothing but a tape measure, using the US Navy circumference method. Enter neck, waist (and hip for women) measurements to get your body fat percentage and fitness category.
Your measurements are processed in the browser and never uploaded. Body measurements are personal data, and they stay that way here.
Results are estimates for general information only and are not medical advice. Talk to a healthcare professional before making significant changes to your diet or exercise.
How to use it
- Take your measurements with a flexible tape, relaxed and level.
- Enter height, neck and waist (and hip, for women).
- Read your estimated body-fat percentage.
The US Navy method
This uses circumference measurements and a logarithmic formula developed for the US Navy. It requires no calipers and no equipment beyond a tape measure.
Accuracy is typically within 3–4 percentage points of a DEXA scan for most people — good enough to track a trend over months, not precise enough to obsess over week to week.
A worked example
Male, 178 cm, waist 88 cm, neck 38 cm:
The formula returns approximately 18.7% body fat.
Measure the waist two centimeters higher or lower and the result shifts by roughly a full percentage point. That sensitivity is why measuring at the same landmark, at the same time of day, matters more than the absolute number does.
Common mistakes
- Pulling the tape tight. It should sit flat against the skin without compressing it.
- Measuring at different points on different days, which creates changes that are not real.
- Measuring after a large meal or late in the day, when abdominal circumference is naturally larger.
Questions people ask
How accurate is this compared with a DEXA scan?
Circumference methods typically land within 3–4 percentage points for people of average build. They are less reliable at the very lean and very heavy extremes.
What is a healthy body-fat percentage?
Commonly cited ranges are roughly 10–20% for men and 18–28% for women, varying with age and source. Essential fat sits well below both.
When should I measure?
First thing in the morning, before eating, in the same conditions each time. Consistency matters more than the time you choose.