Body Fat Calculator
Want a quick body fat estimate? Enter neck, waist, hips, and height and you will get your percentage with the US Navy method. No lab needed.
TL;DR
- The US Navy method uses neck, waist, and hip measurements with height
- US Navy Formula Equations: Men: %Fat = 86.010 × log10(Waist - Neck) - 70.041 × log10(Height) + 36.76
- Example: Male Adult Measurement
How it works
The US Navy method uses neck, waist, and hip measurements with height. A logarithmic formula turns those numbers into body fat percentage.
The math
The formula uses log ratios of waist to neck or waist plus hip minus neck, compared to height.
All measurements must be in centimeters (or scaled accordingly in inches). Subtracting neck circumference compensates for natural skeletal frame thickness.
Examples
Example: Male Adult Measurement
- Height: 178 cm, Waist: 84 cm, Neck: 38 cm, Total Weight: 80 kg
- Waist - Neck difference: 84 - 38 = 46 cm (33.07 - 14.96 = 18.11 in)
- Apply log10 terms: 86.010 × log10(18.11) - 70.041 × log10(70.08) + 36.76
- Calculation: (86.010 × 1.2579) - (70.041 × 1.8456) + 36.76 = 108.19 - 129.27 + 36.76 = 15.68%
- Body Fat: 15.7% | Lean Mass: 67.5 kg | Fat Mass: 12.5 kg.
When to use it
✦ Tracking Body Recomposition Progress
Monitor whether weight loss comes from fat loss rather than muscle tissue reduction.
✦ Establishing Health Category Baselines
Classify body composition into Essential Fat, Athletes, Fitness, Acceptable, or Obesity categories.
✦ Non-Invasive Personal Tracking
Avoid expensive hydrostatic weighing tanks or DEXA scans with reliable home measuring tape readings.
⚠ Common mistakes
- Sucking in the Stomach: Pulling in your stomach distorts waist measurements and gives artificially low fat readings.
- Inconsistent Tape Tension: Pulling the tape too tightly compresses subcutaneous fat; keep tape flat and level.
FAQ (6)
What is a healthy body fat percentage for men and women?
For men, 10-20% is typical for fitness and health. For women, 18-28% is optimal.
How often should I measure my body fat?
Measuring every 2 to 4 weeks provides clear trends without daily water retention fluctuations.
What happens to my weight, height or other health data?
It never leaves your phone. BMI, BMR, body-fat — all computed on-device, no upload, no account. That's intentional for health data: you can check a BMI of 22.8 or a TDEE of 2,100 kcal without worrying about a server log. Closing the tab clears the form from memory.
Does it work offline at the gym or on a plane?
Yep. Once the page has loaded, the calculators are fully offline-first. I've used the pace and BMI tools in airplane mode between flights — no spinner, no retry, just instant numbers. Same for sleep cycles if you're planning a shift.
Can my doctor rely on these numbers?
They're solid estimates using published formulas (WHO for BMI, Mifflin-St Jeor for BMR, CKD-EPI for GFR) but they're not a diagnosis. Think of them as a conversation starter: good for tracking trends, but your GP or nephrologist should interpret GFR, heart age or pregnancy dates with labs and context. We link the sources at the bottom for that reason.
How can I share my result with a trainer or doctor?
Use 'Share Link' in the results panel. It builds a URL with your inputs — for example BMI 70kg/175cm — so they see exactly what you entered. No data is stored on our side, the link just carries the numbers.
Sources & References
⚠ Health Disclaimer
This tool provides estimates for informational purposes only and does not constitute medical, veterinary, or professional advice. Always consult a qualified healthcare professional before making decisions about your health or treatment.