What is a Body Fat Calculator?
A Body Fat Calculator estimates the percentage of your total body weight that is fat, compared with lean mass (muscle, bones, organs and water). Weight and BMI (Body Mass Index) are common measures, but they cannot tell fat from muscle. For example, a muscular person can have a high BMI and a low body fat percentage. A body fat estimate adds a different view of body composition.
Body fat percentage matters because carrying a high amount of body fat, especially around the abdomen, is associated with higher risk of conditions such as cardiovascular disease and type 2 diabetes. Very low body fat can also be a problem, as it can affect hormones and bone health. Treat the result from this calculator as an estimate, not a diagnosis.
Essential Fat:
The body needs a minimum amount of fat to function. Commonly cited essential fat ranges are about 2–5% for men and 10–13% for women. Going below these ranges can be unhealthy.
How Body Fat is Estimated Here: The U.S. Navy Method
This calculator uses the U.S. Navy circumference method. It estimates body fat from body measurements instead of lab equipment. It needs your sex, height, neck and waist measurements, and for women also hip measurements. Weight is used only to split your weight into fat mass and lean mass once the percentage is known.
Men: BF% = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: BF% = 495 ÷ (1.29579 − 0.35004 × log10(waist + hips − neck) + 0.22100 × log10(height)) − 450
All measurements in centimetres. Fat mass = weight × BF% ÷ 100, and lean mass = weight − fat mass.
About the age field: the Navy equation does not use age. This calculator asks for it only to confirm that you are an adult (18 or older), since the method is designed for adults.
Step-by-Step: Getting a More Consistent Result
- Select Male or Female: the equation is different for each, and hip measurement is needed only for the female formula.
- Enter height and weight.
- Waist: measure at the level of the navel for men, and at the narrowest part of the waist for women. Keep the tape level and snug, but do not compress the skin.
- Neck: measure just below the larynx (Adam's apple), with the tape sloping slightly down toward the front.
- Hips (women): measure around the widest part of the hips and buttocks.
Tip:
Measure at the same time of day and in the same way each time, for example in the morning before eating. Small changes in tape position change the result noticeably, so consistency matters more than any single reading.
Interpreting Your Result
The category shown next to your result follows the commonly used American Council on Exercise (ACE) ranges:
| Category | Men | Women |
|---|
| Essential fat | 2–5% | 10–13% |
| Athlete | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and above | 32% and above |
These ranges are general guides. They are not a diagnosis, and health depends on much more than a single percentage.
Limits of Body Fat Estimates
- It is an estimate. Studies comparing the Navy method with DEXA scans report that it can be close to the DEXA value for many people on average, but the error for an individual can be several percentage points.
- Measurement technique matters. A few millimetres of difference in neck or waist measurement can shift the result.
- Body shape differs. People with unusually large muscles, or unusual fat distribution, may get results that are less accurate.
- Different methods give different numbers. Navy measurements, bioimpedance scales, skinfold calipers and DEXA scans can all disagree. Use the same method over time if you want to track change.
- Age is not part of the equation. Body composition changes with age, for example muscle mass tends to decline, but this calculator does not adjust for it.
Use for Tracking, Not Diagnosis:
A single estimate cannot tell you whether you are healthy. If you are worried about your weight or body composition, speak to a doctor or registered dietitian.
Medical Disclaimer:
This tool provides an estimate based on a mathematical formula and is for general information only. For a clinical-grade assessment, consult a medical professional, who can arrange a method such as a DEXA scan. Do not use this tool if you are under 18 or pregnant, or if you have or may have an eating disorder.