Calculator
How it works and when to use it
The calculator uses the Hodgdon and Beckett equations known as the US Navy method, which estimate body density from the neck, waist (and hips for women) and height, then turn it into body fat with the Siri equation.
Men measure the waist at the navel, women at the narrowest point and the hips at the widest, the neck just below the larynx, best in the morning with the tape snug but not tight.
Reference: Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center reports 84-11 and 84-29 (1984); metric form with Siri: %BF = 495 / density − 450
Frequently asked questions
How accurate is it?
It is an estimate that can differ by a few points from DEXA or body composition scales, but it is useful to follow change in one person measured the same way.
What is a normal body fat percentage?
It depends on age and sex, women naturally carry more than men, and there is no single agreed set of cut-offs, so the calculator shows the number and your doctor or dietitian reads it.
Why measure fat and not just weight?
Weight does not tell fat from muscle, so with exercise the scale may move a little while fat drops clearly.
Tools you may also need
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- Ideal weight calculator The lowest and highest healthy weight for your height, and what to lose or gain.
- Macro calculator Grams of carbs, protein and fat a day and per meal.
- Water intake calculator Total water a day, and the share to drink.
- Protein calculator Grams of protein a day and per kilogram of your weight.
- Body mass index (BMI) calculator Your BMI, its class and the healthy weight for your height.
Clinic software for this specialty
Try Clinicato for your clinic
These calculators are free here for everyone, and in Clinicato 49 medical tools work inside the patient's file with the "Medical tools" add-on: filled from the visit and the vital signs, with the result added to the visit's plan, next to appointments, prescriptions and invoices.