What is body fat percentage?

Body fat percentage is the proportion of your total body weight that is fat tissue, as opposed to muscle, bone, organs, and water (collectively called lean body mass). It's a far more meaningful health metric than weight alone or BMI, because two people can have the same weight but very different body compositions. A muscular athlete and a sedentary person both at 80 kg may have body fat percentages of 12% and 28% respectively - drastically different health profiles. This calculator uses the US Navy body fat circumference method (developed by Hodgdon and Beckett in 1984), which uses simple tape measurements at the neck, waist, and hip (women only) along with height. Accuracy is typically within 3-4% of more sophisticated methods like DEXA scan.

How to use this tool

1. Choose unit system — Metric (cm) or Imperial (inches).
2. Select sex — Male or female - the formulas and measurement requirements differ. Women need hip measurement; men don't.
3. Measure height accurately — Stand barefoot against a wall, look forward, measure from top of head to floor.
4. Measure waist — Men: at navel level. Women: at the narrowest point of waist (above belly button). Tape snug but not tight, do not suck in stomach.
5. Measure neck — Just below the larynx (Adam's apple), looking straight ahead. Tape horizontal.
6. Measure hip (women only) — At the widest point of the hips/buttocks. Stand straight, weight even on both feet.
7. Read your body fat % — Result shown with category (Essential / Athletes / Fitness / Average / Above average) based on US Navy standards.

US Navy formula

Men: Body fat % = 86.010 × log₁₀(waist - neck) - 70.041 × log₁₀(height) + 36.76

Women: Body fat % = 163.205 × log₁₀(waist + hip - neck) - 97.684 × log₁₀(height) - 78.387

All measurements in inches. Metric values are converted internally.

The formula works because fat is preferentially distributed in specific locations (belly, hips, neck) which correlate with total body fat in a predictable way for each sex.

Examples

Body fat ranges (US Navy categories):

• Men - Essential: 2-5% (athletic competitors only, not sustainable)
• Men - Athletes: 6-13% (visible abs, very fit)
• Men - Fitness: 14-17% (lean and toned)
• Men - Average: 18-24% (typical adult man)
• Men - Above average: 25%+ (higher health risk)
• Women - Essential: 10-13% (typical of athletes)
• Women - Athletes: 14-20% (visible muscle definition)
• Women - Fitness: 21-24% (lean and toned)
• Women - Average: 25-31% (typical adult woman)
• Women - Above average: 32%+ (higher health risk)

Tips & best practices

• Measure in the morning, on an empty stomach, after bathroom - consistency matters more than absolute value
• Use a soft flexible tape (cloth or tailor's tape) - rigid metal tapes bend incorrectly around curves
• Don't pull the tape tight - it should rest gently on skin without creating indentation
• Take 3 measurements at each location, use the average - reduces measurement error
• Track changes over weeks, not days - body fat doesn't change overnight
• Combine with weight tracking - if weight is stable but body fat drops, you're gaining muscle (great outcome!)
• Women: hip measurement varies with menstrual cycle (water retention) - measure on the same week of cycle each time

Limitations & notes

US Navy method is accurate to within 3-4% for most people but has limitations: (1) less accurate for people with unusual fat distribution (e.g. mostly limb fat, less torso fat), (2) older adults often have higher torso fat for the same body fat % - method may underestimate, (3) very lean athletes may show negative or near-zero - formula isn't designed for elite athletic body comp. For maximum precision, use DEXA scan (gold standard, ±1% accuracy), hydrostatic weighing, or BodPod. Bioelectrical impedance scales are convenient but have ±5-8% error.

Frequently Asked Questions

What's a healthy body fat percentage?

For men: 14-17% is fitness range, 18-24% is average and acceptable, above 25% indicates higher metabolic risk. For women: 21-24% is fitness range, 25-31% is average, above 32% is higher risk. Essential body fat (2-5% men, 10-13% women) is needed for organs and hormones - going lower is dangerous.

How accurate is the US Navy method?

Studies show ±3-4% accuracy compared to gold-standard DEXA scans. Better than BIA scales (5-8% error) but not as accurate as DEXA (±1%). The simplicity (just 3-4 tape measurements) and free availability make it the most practical method for home tracking.

How do I measure my waist correctly?

Men: measure at the navel level. Women: at the narrowest point of waist (above belly button). Stand normally, breathing relaxed (don't suck in stomach), arms at sides. Tape should be horizontal, gently touching skin without indenting.

Should I lose body fat or just lose weight?

Focus on body fat percentage, not just weight. Losing weight without strength training causes 25-30% of the loss to come from muscle - bad outcome. Combine moderate calorie deficit with strength training to lose fat while preserving (or building) muscle. The ideal metric is your body fat % over time, not the scale.

How fast can I lose body fat?

Sustainable rate: 0.5-1% body fat per month with moderate calorie deficit + strength training. Faster rates (over 2%/month) usually indicate muscle loss too. Crash diets cause rapid initial loss (mostly water) followed by metabolic adaptation and rebound. Slow and steady wins.

Why is my body fat % higher than my BMI category suggests?

BMI doesn't measure body composition - just weight relative to height. A normal-BMI person can have high body fat (skinny-fat) while a high-BMI athlete can have low body fat. Always trust body fat % over BMI for body composition assessment.

Are bathroom 'body fat scales' accurate?

BIA (bioelectrical impedance) scales pass a tiny electrical current through your body and estimate fat from resistance. Accuracy is ±5-8% under ideal conditions but is heavily affected by hydration, time of day, food intake, body temperature. Use for trend tracking (measure same time/conditions each day) not absolute values.

Related tools

BMI Calculator · Lean Body Mass · BMR Calculator