Body Fat Percentage

Body fat percentage is the proportion of your total body weight that comes from fat tissue, as opposed to muscle, bone, organs, and water. It's one of the most widely used measures of body composition because it tells you something BMI cannot: whether a given body weight is made up mostly of fat or mostly of lean tissue. You can estimate yours with the Body Fat Calculator.

Because directly measuring fat mass requires expensive lab equipment like DEXA scans or hydrostatic weighing, most everyday estimates rely on indirect methods. The two most common are circumference-based formulas, such as the one used in the Navy Body Fat Calculator and the Army Body Fat Calculator, and skinfold caliper methods, used in the Skinfold Body Fat Calculator. Both trade some accuracy for convenience and repeatability.

Body fat percentage matters for more than aesthetics — it's used to assess health risk, set nutrition and training targets, and calculate related figures like lean body mass. Tracking it over weeks or months, using the same measurement method each time, gives a much clearer picture of body composition change than tracking scale weight alone.

The general formula behind body fat percentage is:

Body Fat Percentage = (Fat Mass ÷ Total Body Weight) × 100

Since fat mass usually isn't measured directly outside a lab, practical methods estimate it differently. The Navy method, for example, uses circumference measurements in a logarithmic formula:

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

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

(all measurements in the same unit, typically centimeters or inches, entered consistently)

Skinfold methods instead sum caliper readings at several body sites and apply a population-specific regression equation to estimate body density, which is then converted to a percentage.

A man with a waist of 85 cm, neck of 38 cm, and height of 178 cm using the Navy method:

log₁₀(85 − 38) = log₁₀(47) ≈ 1.672 log₁₀(178) ≈ 2.250

BF% = 495 ÷ (1.0324 − 0.19077 × 1.672 + 0.15456 × 2.250) − 450 BF% = 495 ÷ (1.0324 − 0.3190 + 0.3478) − 450 BF% = 495 ÷ 1.0612 − 450 BF% = 466.5 − 450 = 16.5%

This falls within the healthy range for an adult male.

• Method choice affects the result. Circumference methods and skinfold methods can disagree by 2 to 5 percentage points for the same person, so stick to one method when tracking change over time.
• It's the basis for lean body mass. Once you know body fat percentage, subtracting fat mass from total weight gives Lean Body Mass, a figure often used to set protein and training targets.
• Fat distribution matters, not just total amount. Two people with the same body fat percentage can carry it differently, which is part of why Waist-to-Hip Ratio is used alongside body fat percentage to assess health risk.
• Essential fat is a hard floor. Every method assumes some minimum essential fat level, and estimates below roughly 3 to 5 percent for men or 10 to 13 percent for women should be treated with skepticism.
• Hydration and measurement timing affect accuracy. Circumference and skinfold readings can shift slightly with hydration status and time of day, so measuring under similar conditions each time improves consistency.