Body Fat Calculator — US Navy & BMI Method
Estimate your body fat percentage, fat mass, and lean mass using the US Navy circumference method, with a BMI-method estimate alongside. Metric and imperial units, plus a fat-to-lose goal.
How to use the Body Fat Calculator
- Choose Units & Gender: Go to fixflowhub.com/body-fat-calculator, choose metric or imperial units, and select your gender
- Enter Age, Height & Weight: Set your age, height, and weight with the sliders
- Enter Circumferences: Measure and enter your neck and waist (and hip if female)
- View Results: See your body fat percentage, category, fat mass, lean mass, and a BMI-method estimate instantly
Frequently Asked Questions
What is a healthy body fat percentage?
For men, 10–20% is considered fit; essential fat is 2–5% and athletes are typically 6–13%. For women, 18–28% is considered fit; essential fat is 10–13% and athletes are typically 14–20%.
How accurate is an online body fat calculator?
Calculators using the US Navy circumference method are about 80–85% accurate — typically within 3–4% body fat. The BMI method is a rougher estimate. For precise measurement, a DEXA scan or hydrostatic weighing is more accurate but requires clinical equipment.
What is the difference between the US Navy method and the BMI method?
The US Navy method estimates body fat from neck, waist, and (for women) hip measurements plus height, which correlates closely with body composition. The BMI method estimates body fat from BMI, age, and gender — no tape measure needed, but less accurate. FixFlowHub shows both so you can compare.
What are fat mass and lean mass?
Fat mass is your total body-fat weight (body weight × body-fat %). Lean mass is everything else — muscle, bone, organs, and water. The goal during a diet is to lose fat mass while preserving lean mass.
How can I reduce body fat percentage?
Combine a moderate calorie deficit with strength training and cardio. Losing 0.5–1% body fat per month is a realistic and sustainable goal; prioritise protein to preserve lean mass.