Body Fat Calculator — US Navy Method (Neck, Waist & Hip)

Body fat percentage estimates how much of your weight is fat versus lean mass. Unlike BMI alone, the US Navy circumference method uses neck, waist, and (for women) hip measurements with height to produce a practical field estimate. This free calculator returns your body fat % and a fitness category so you can track composition trends — not just scale weight.

How to Use the Body Fat Calculator

You only need a soft measuring tape and a few minutes:

Select gender and enter age, weight (kg), and height (cm).
Measure circumferences — neck and waist for everyone; hip is required for women.
Enter measurements in centimetres and click Calculate body fat.
Read your % and category badge (Essential, Athletes, Fitness, Average, or Obese).

Example: Male, height 175 cm, waist 85 cm, neck 38 cm. Plugging these into the US Navy male formula typically yields about 15–17% body fat (Fitness / Athletes border depending on rounding). Enter the same values above to see the exact rounded percentage. All math runs in your browser.

What Is Body Fat Percentage and Why It Matters

Body fat percentage is the share of total mass that is adipose tissue. Two people can share the same weight and BMI yet differ sharply in fat vs muscle. Tracking body fat helps interpret weight change during a cut or bulk and flags visceral risk better than the scale alone when paired with waist trends.

Category (general guide)	Men (approx.)	Women (approx.)
Essential	< 6%	< 14%
Athletes	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
Obese	25%+	32%+

These bands match the labels used in this calculator. Individual health advice still depends on age, medical history, and professional assessment. Pair results with a BMI calculator and a calorie & macro calculator when setting nutrition goals.

US Navy Formula with a Worked Example

Male formula:

%BF = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450

Female formula:

%BF = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450

All lengths are in centimetres; log₁₀ is base-10 logarithm.

Worked male example:

Height = 175 cm; waist = 85 cm; neck = 38 cm
waist − neck = 47
log₁₀(47) ≈ 1.672; log₁₀(175) ≈ 2.243
Denominator ≈ 1.0324 − 0.19077×1.672 + 0.15456×2.243 ≈ 1.060
495 ÷ 1.060 ≈ 467; 467 − 450 ≈ 17% (tool may round slightly differently)

Women substitute waist + hip − neck inside the first log term and use the female constants. Accurate tape placement matters more than calculator precision.

Important Limitations & Common Mistakes

Common measurement pitfalls:

Wrong landmarks: Measuring waist at the belt line instead of the Navy landmark can shift results by several points.
Skipping hip for women: The female equation requires hip; omitting it invalidates the estimate.
Treating Navy % as DEXA: Field formulas estimate; lab methods remain the gold standard for clinical decisions.
Ignoring hydration and posture: Measure at a consistent time of day with relaxed posture for comparable trends.

Frequently Asked Questions

What method does this body fat calculator use?

The US Navy circumference method. It estimates body fat from height plus neck and waist for men, and height plus neck, waist, and hip for women, using logarithms in the official-style formulas.

How accurate is the US Navy body fat method?

It is a field estimate — typically within a few percentage points for many adults when measured carefully. DEXA, Bod Pod, or hydrostatic weighing are more precise. Use consistent tape technique to track trends over time.

Where should I measure neck, waist, and hips?

Neck: just below the larynx, tape sloping slightly downward. Waist (men): at navel level; women often at the narrowest point per protocol guidance. Hips (women): at the widest point of the buttocks. Keep the tape snug, not compressing skin.

What is a healthy body fat percentage?

Rough adult guides: men often fall in “fitness/average” around the mid-teens to mid-20s; women typically higher essential-fat needs, with fitness/average often spanning roughly the low-20s to low-30s. Categories in this tool label Essential, Athletes, Fitness, Average, and Obese ranges.

Why is BMI not enough?

BMI only uses height and weight. Muscular people can show a high BMI with low body fat. Pair BMI with body fat % — try our BMI Calculator alongside this tool.

Do I need hip measurement as a man?

The Navy male formula uses waist and neck with height — hip is not required. Hip is required for the female formula.

Example: male 175 cm, waist 85 cm, neck 38 cm — what body fat?

Using the male Navy formula, that combination often lands near the mid-to-high teens (around ~15–18% depending on exact logs). Enter the same numbers in the form above for the precise rounded result.

Can athletes use this calculator?

Yes for screening, but very lean or very muscular physiques may see larger error vs lab methods. Treat the number as a trend tool, not a medical diagnosis.

How often should I remeasure?

Every 2–4 weeks under similar conditions (time of day, hydration, same tape landmarks). Daily fluctuations are mostly water and measurement noise.

Is this body fat calculator free?

Yes. Free, no signup, and calculated in your browser for privacy.