健康・フィットネス

体脂肪率計算機

Navy法またはBMI法で体脂肪率を推定

使い方
  1. Select your Gender and enter your 年齢.
  2. Provide your 体重 (kg) and 身長 (cm).
  3. Measure your Neck and Waist in cm. Women must also provide their Hip measurement.
  4. Click Calculate Body Fat to see your estimated body composition.

計算式

This calculator uses the highly regarded U.S. Navy Method. It estimates body fat percentage using circumferences rather than complex equipment.

Categories (general estimates):

  • Essential Fat: Men 2-5%, Women 10-13%
  • Athletes: Men 6-13%, Women 14-20%
  • Fitness: Men 14-17%, Women 21-24%
  • Average: Men 18-24%, Women 25-31%
  • Obese: Men 25%+, Women 32%+

What Is Body Fat Percentage and Why Does It Matter?

Body fat percentage (BF%) is the proportion of your total body weight that consists of adipose tissue (fat). Unlike BMI, which only considers height and weight, body fat percentage directly quantifies how much of your body is fat versus lean mass—muscle, bone, water, and organs. This makes it a far more precise indicator of metabolic health and fitness level.

Having too much body fat—particularly visceral fat (fat surrounding internal organs)—is strongly linked to insulin resistance, type 2 diabetes, cardiovascular disease, and chronic inflammation. Conversely, body fat that falls below essential levels impairs hormone production, immune function, and organ protection. The Wikipedia article on body fat percentage covers the full spectrum of measurement methods and health implications.

The U.S. Navy Method: How This Calculator Works

This calculator uses the U.S. Navy circumference method, developed by Hodgdon and Beckett (1984) for the U.S. Naval Health Research Center. It estimates body fat using only a tape measure—no expensive equipment required—and has been validated against underwater weighing with strong correlation (r ≥0.90).

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Men: Measure neck and waist at the narrowest points
Women: Measure neck, waist (narrowest), and hips (widest)
All measurements in cm; take at least 2 readings and average them for accuracy.

While the Navy method is convenient and sufficiently accurate for most people, more precise methods include DEXA scanning (gold standard), hydrostatic weighing, air displacement plethysmography (Bod Pod), and skinfold calipers. For population screening and home tracking, the Navy method offers an excellent accuracy-to-convenience ratio.

Healthy Body Fat Ranges: What the Categories Mean

The American Council on Exercise (ACE) classifies body fat into five categories for adults:

Essential Fat
Men: 2–5%  |  Women: 10–13%

Minimum fat required for survival, hormonal function, and organ insulation. Not maintainable long-term.

Athletes
Men: 6–13%  |  Women: 14–20%

Typical of competitive athletes and serious fitness enthusiasts. Associated with peak performance.

Fitness
Men: 14–17%  |  Women: 21–24%

Above average fitness. Generally healthy, with good cardiovascular and metabolic markers.

Average
Men: 18–24%  |  Women: 25–31%

Acceptable for general health, though the higher end of this range warrants lifestyle attention.

肥満
Men: 25%+  |  Women: 32%+

Elevated health risk. Medical consultation and structured lifestyle intervention recommended.

How to Reduce Body Fat: Evidence-Based Strategies

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Caloric Deficit + High Protein — A 300–500 kcal/day deficit drives fat loss. Adequate protein (1.6–2.4 g/kg body weight) preserves lean mass during a cut. Use our カロリー計算機 to find your target.
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Resistance Training — Builds or maintains muscle while losing fat, improving body composition even when the scale doesn't move. Compound lifts (squat, deadlift, bench press) maximise hormonal response.
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Cardiovascular Exercise — HIIT (High-Intensity Interval Training) burns more calories in less time and generates excess post-exercise oxygen consumption (EPOC), elevating metabolism for hours post-workout.
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Sleep Optimisation — Chronic poor sleep disrupts leptin and ghrelin (hunger hormones), increasing fat storage and appetite. Aim for 7–9 hours per night of consistent quality sleep.

Frequently Asked Questions About Body Fat

Is body fat percentage more accurate than BMI?

For assessing actual body composition, yes. BMI can misclassify muscular athletes as overweight and skinny-fat individuals as healthy. Body fat percentage directly quantifies the fat-to-lean mass ratio. However, BMI remains useful as a quick population-level screening tool. Using both together gives the most complete picture.

How often should I measure body fat?

Monthly measurements are ideal for tracking trends without being misled by day-to-day fluctuations. Consistency matters: always measure at the same time of day (morning, before eating), under the same conditions, and with the same method to ensure comparable readings.

Can I spot-reduce fat in specific areas?

No—spot reduction is a well-debunked myth. The body draws on fat stores systemically based on genetics and hormonal factors, not which muscles are being worked. Abdominal exercises strengthen core muscles but do not selectively burn belly fat. A caloric deficit combined with exercise reduces body fat overall.

Related Health Calculators

⚖️
BMI計算機Classify weight status using height & weight
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カロリー計算機Set daily intake for fat loss or muscle gain
 ⚡
基礎代謝計算機Your resting calorie burn at complete rest
 📊
1日の総消費カロリー計算機Total energy expenditure with activity level
 🎯
理想体重計算機Evidence-based healthy weight range for your height

References & Further Reading

  1. Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, 1984.
  2. Wikipedia contributors. 体脂肪率. Wikipedia, The Free Encyclopedia.
  3. American Council on Exercise. ACE Body Fat Percentage Chart. ACE Fitness.
  4. Fleck SJ. Body composition of elite American athletes. Am J Sports Med, 1983.