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Body Fat Calculator

Estimate body fat percentage with the US Navy method — just a tape measure and the right spots.

Body fat percentage

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Fat mass

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Lean mass

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Healthy range

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For general information only, not medical advice. Sustainable, gradual targets work best. Consult a doctor or registered dietitian for personal guidance, especially if you have a health condition or are pregnant.

How the US Navy body fat method works

The US Navy formula was developed by the Naval Health Research Center to give servicemembers a simple body composition test that needs only a tape measure. It's not as precise as a DEXA scan but it's repeatable, free and within about 3-4 percentage points of lab measurement for most adults — accurate enough to track changes over time, which is what really matters.

The two formulas (imperial inches)

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

The calculator above handles both units automatically — measurements are converted to inches internally.

Getting the measurements right

Accuracy is mostly about consistent measurement. A few practical tips:

  • Neck. Right below the larynx (Adam's apple for men). Tape horizontal, not at an angle. Look straight ahead, shoulders relaxed.
  • Waist (men). Around the navel.
  • Waist (women). At the narrowest point — typically just above the navel.
  • Hip (women only). Widest point around the buttocks. Feet together.
  • Posture. Stand relaxed, exhale gently, don't suck in. Same time of day for repeated measurements (mornings are best).

Reading the result

The American Council on Exercise body fat categories used here:

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

"Essential" is the minimum the body needs to function. The "fitness" band is where most regularly active adults sit. "Above average" is where US adult averages have drifted in recent decades.

Body fat % vs. BMI

BMI is simpler — just height and weight — but doesn't distinguish muscle from fat. A muscular athlete can register as "overweight" on BMI with very low body fat. Body fat percentage measures what BMI tries to proxy. Use both: BMI for a quick general screen (and what insurers look at), body fat % for what's actually going on. The BMI calculator and this tool together are a much better signal than either alone.

What to do with the number

Focus on the trend, not the single reading. Take measurements monthly under similar conditions and watch the direction over a few months. To plan calorie and protein intake for a body fat goal, pair this with the calorie calculator and macro calculator.

Frequently asked questions

How accurate is the US Navy body fat method?

For most people it estimates body fat to within about 3-4 percentage points of the gold-standard DEXA scan. It is less accurate at the extremes (very lean athletes or very high body fat) but is by far the most accessible no-equipment method.

How do I take the measurements correctly?

Neck: just below the larynx, tape level. Waist: men at the navel, women at the narrowest point. Hip (women only): widest point around the buttocks. Keep the tape level, snug but not compressing the skin, and exhale gently before reading.

What is a healthy body fat percentage?

For men, 14-24% is the typical "fitness" to "average" range, with under 10% considered very lean. For women, 21-31% is typical, with under 18% considered very lean. Essential fat (the minimum the body needs) is around 2-5% for men and 10-13% for women.

Why does the women's formula need hip measurement?

Women tend to carry fat in the hips and thighs as well as the abdomen, so a single waist measurement misses too much. Adding hip improves accuracy. Men carry abdominal fat more uniformly so waist plus neck is enough.

Is BMI better than body fat percentage?

BMI is simpler — only height and weight — but it doesn't distinguish muscle from fat. A muscular athlete can be "overweight" by BMI with low body fat. Body fat percentage measures what BMI tries to proxy. The two together give a fuller picture.

Can I track changes over time?

Yes, and the trend is more reliable than any single measurement. Measure under similar conditions (morning, fasted, after the bathroom) and look at month-over-month changes rather than week-to-week noise.

Worked example

A male, 70 in (178 cm) tall, neck 15 in (38 cm), waist 33.5 in (85 cm), weight 176 lb (80 kg).

  • BF% = 86.010 × log10(33.5 − 15) − 70.041 × log10(70) + 36.76
  • = 86.010 × 1.2672 − 70.041 × 1.8451 + 36.76
  • = 108.99 − 129.23 + 36.76 = ~16.5%
  • Category: Fitness
  • Fat mass: 80 × 0.165 ≈ 13.2 kg · Lean mass: 80 − 13.2 ≈ 66.8 kg

A waist reduction of 1 inch (2.5 cm) at this height — same neck, same height — drops body fat to about 13.6%, well into the athlete band.

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