Body Fat Calculator - Body Fat Percentage

Your Measurements

Estimate body fat percentage from neck, waist, and hip measurements with the equations the US Navy used until December 2025. See lean mass and set a target.

Choose Your Sex

Enter Height

Measure Neck

Measure Waist

This estimate uses the circumference equations of Hodgdon and Friedl (1999), which the US Navy used until December 2025. In a 2024 study of 1,904 US soldiers, they read on average 4.8 points below a DEXA scan for men and 1.7 points below for women. It is a screening estimate, not a diagnosis; a DEXA scan or underwater weighing measures body fat more directly.

Formulas and sources

Each formula this calculator uses, where it comes from, and what it leaves out. "How it works" shows the same formula with your own numbers.

Body fat percentage, men

For men

BF% = 86.01 × log10(waist - neck) - 70.041 × log10(height) + 36.76
BF%
body fat percentage
waist
waist at the navel, in inches
neck
neck just below the Adam's apple (larynx), in inches
height
height in inches

log10 is the base-10 logarithm. Centimeters are converted to inches first (÷ 2.54). Rounded to a whole percent, the equation gives each percentage in the men's table of the Navy's Guide 4 (January 2023), and every cell checked in the February 2025 edition [2].

Source: Uses the formula in Hodgdon and Friedl (1999) [1], which the US Navy used until December 2025 [2]. Taylor and colleagues (2024) compare it with DEXA scans [3]. The conversion factor is NIST's [4].

Body fat percentage, women

For women

BF% = 163.205 × log10(waist + hip - neck) - 97.684 × log10(height) - 78.387
BF%
body fat percentage
waist
waist at its narrowest point, in inches
hip
hips at the widest point of the buttocks, in inches
neck
neck just below the Adam's apple (larynx), in inches
height
height in inches

Rounded to a whole percent, it gives each percentage in the women's table of Guide 4, January 2023 and February 2025 editions [2].

Source: Uses the formula in Hodgdon and Friedl (1999) [1], as for men.

Fat mass, lean mass and target weight

When a weight is entered

fat mass = weight × BF% ÷ 100
fat mass
the weight of body fat
weight
your weight, in the unit you enter
BF%
body fat percentage, from the equation above

Lean mass is weight minus fat mass. With a target, target weight = lean mass ÷ (1 - target BF% ÷ 100), and fat to lose is weight minus target weight. Both assume lean mass stays the same.

Source: Standard formula; no single publisher.

Body fat categories

Essential Fat
men below 6.0%, women below 14.0%
Athletic
men 6.0% to 13.9%, women 14.0% to 20.9%
Fitness
men 14.0% to 17.9%, women 21.0% to 24.9%
Average
men 18.0% to 24.9%, women 25.0% to 31.9%
Obesity
men 25.0% or more, women 32.0% or more

The American Council on Exercise (ACE) lists whole-number ranges with gaps. Here each band runs to the next one's lower figure and is read on the percentage shown. ACE's Athletes and Acceptable are called Athletic and Average; its Obesity starts above 25% (men) and 32% (women). Essential Fat also covers results below ACE's lowest figures. ACE does not call any range healthy.

Source: Based on ACE's body fat norms [5], adapted as the note says.

Sources

  1. Hodgdon JA, Friedl K. Development of the DoD Body Composition Estimation Equations. Naval Health Research Center, Technical Document 99-2B, 1999 (DTIC ADA370158).
  2. US Navy, OPNAV N171 Physical Readiness Program. Guide 4: Body Composition Assessment (BCA), Tables 2 and 3 in the first two; the two-step method in the third. January 2023, February 2025 and December 2025 editions.
  3. Taylor KM, Castellani MP, Bartlett PM, Oliver TE, McClung HL. Development and cross-validation of a circumference-based predictive equation to estimate body fat in an active population, section 3.6 and Table 3. Obesity Science & Practice, 2024; 10(2): e747.
  4. National Institute of Standards and Technology. NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science, length and mass. Special Publication 811.
  5. American Council on Exercise. Percent Body Fat Norms for Men and Women, table on the Percent Body Fat Calculator page. Archived copy of December 1, 2023; no longer on ACE's website.

What this calculator does not cover

  • It estimates body fat from tape measurements. Underwater weighing and DEXA scans (low-dose X-ray body scans) measure it more directly.
  • In a 2024 study of 1,904 US soldiers, these equations read on average 4.8 percentage points below DEXA for men and 1.7 below for women, and single readings varied more [3].
  • The equations were fitted on 594 men and 202 women measured in the US Navy [1]. Age does not enter the equations or the categories.
  • It does not model the Navy's two-step method, which replaced these equations from January 2026. That method screens by waist-to-height ratio, then reads body fat from tables of weight and height minus waist [2].
  • A result between 0% and 2% is shown as 2.0%, and a result of 0% or less is shown as invalid measurements.

Sources checked on .

Help

Quick Start Guide

  1. Choose Your Sex: Pick Male or Female: the equations differ, and the female equation adds the hip measurement. Age is optional.
  2. Enter Height: Input your height in the selected unit system (metric or imperial).
  3. Measure Neck: Measure your neck just below the Adam's apple, with the tape level, and enter the value.
  4. Measure Waist: Men measure the waist at the navel; women measure it at the narrowest point.
  5. Measure Hips (Women): For women, measure around the widest part of your hips and enter the value.
  6. View Results: See your estimated body fat percentage and category (athletic, fitness, average, etc.).
  7. Optionally Set a Target: Set a target body fat percentage for goal tracking.

Frequently Asked Questions

Neither is more accurate overall, because they measure different things. BMI compares weight with height and cannot tell muscle from fat. The equations the US Navy used until December 2025 estimate body fat from tape measurements of the neck, waist and, for women, hips.

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