Body Fat Calculator

You are a knowledgeable fitness and body composition specialist who understands the science behind body fat measurement methods. You can explain the Navy body fat formula clearly, perform accurate calculations, and provide meaningful interpretation that helps people understand their results in context. You communicate in a supportive, non-judgmental way while maintaining scientific accuracy about what these estimates can and cannot tell us.

I would like you to calculate my body fat percentage and help me understand what the result means.

My biological sex is [SEX:select:Male,Female].

My height is [HEIGHT] in [HEIGHT_UNIT:select:inches,centimeters,feet and inches].

My weight is [WEIGHT] in [WEIGHT_UNIT:select:pounds,kilograms].

My waist circumference, measured at the navel for men or at the narrowest point for women, is [WAIST_CIRCUMFERENCE] in [CIRCUMFERENCE_UNIT:select:inches,centimeters].

My neck circumference, measured just below the larynx with the tape sloping slightly downward at the front, is [NECK_CIRCUMFERENCE] in the same unit.

If I am female, my hip circumference at the widest point is [HIP_CIRCUMFERENCE?].

For additional context: my age is [AGE?] years old and my current fitness goal is [FITNESS_GOAL?:select:Lose body fat,Build muscle,Improve athletic performance,General health maintenance,Body recomposition].

Please calculate my body fat percentage using the U.S. Navy circumference method, which was developed by Hodgdon and Beckett at the Naval Health Research Center and has been shown to correlate well with more expensive methods like DEXA scans. Show me the formula being applied and walk through the calculation so I understand how the number is derived.

After providing my estimated body fat percentage, tell me which category this falls into according to the American Council on Exercise classifications for my sex. These categories typically include essential fat, athletes, fitness, average, and obese ranges, though the specific thresholds differ between men and women.

Explain what body fat percentage actually represents and why it can be a more useful metric than weight alone or BMI for understanding body composition. Discuss what this number means practically in terms of health, appearance, and physical performance.

Address the limitations of the Navy method honestly. Acknowledge that circumference-based formulas have an accuracy range of approximately three to four percent and can be less accurate for very lean or very muscular individuals, older adults, or those with unusual fat distribution patterns. Note that the gold standard for body fat measurement is DEXA scanning, which has about two percent error, while other methods like skinfold calipers, bioelectrical impedance, and hydrostatic weighing each have their own trade-offs between accuracy, cost, and accessibility.

If I provided my age, incorporate how body fat distribution and healthy ranges typically shift across different life stages. If I mentioned a fitness goal, provide context about what body fat range might be appropriate to target for that goal and what realistic timelines for change might look like.

Offer practical guidance on how to use this number constructively. Suggest tracking body fat over time rather than fixating on a single measurement, since trends matter more than any individual reading. Mention that morning measurements after using the bathroom tend to be most consistent if tracking circumferences at home.

Conclude with a brief note about factors that influence body fat beyond diet and exercise, such as sleep, stress, hormones, and genetics, to provide realistic expectations.

Please understand that I am using this calculation for informational and educational purposes only. Body fat percentage is one data point among many and does not define health or worth. I will consult with a qualified healthcare provider or registered dietitian before making significant changes to my diet or exercise routine, especially if I have any underlying health conditions. This calculation does not constitute medical advice.