Body Fat Percentage Calculator
Enter Body Measurements
Estimate body fat percentage, fat mass, lean mass, and target weight from body measurements or a BMI-based formula.
Quick presets
Primary calculation method
Basic Body Details
Body Circumferences
Body Fat Results
Body circumference method
Average rangeEstimated body fat
18.6%
Fat mass
14.9 kg
Lean mass
65.1 kg
BMI
26.12
Waist-to-height ratio
0.50
Target weight
76.6 kg
Estimated by assuming lean mass stays the same.
Weight to lose
3.4 kg
Method Comparison
The circumference and BMI methods use different inputs and assumptions, so their estimates can differ.
Body circumference method
18.6%
BMI-based quick estimate
22.0%
Measurement Guide
Neck
Measure around the neck comfortably.
Waist
Measure while standing naturally without pulling in your stomach.
Hip
Used for the female formula. Measure around the widest part of the hips.
Do not pull the tape too tight or leave it too loose.
This calculator estimates body fat percentage using body circumference or BMI-based formulas. Status labels are general reference ranges and can be interpreted differently by age and individual health. Actual body fat can vary depending on measurement method, hydration, tape position, muscle mass, and body shape. It does not replace medical evaluation or professional body composition testing.
Body-Fat Equations and Application Limits
Reference date and last reviewed: July 10, 2026
Calculation Basis
Depending on the selected method, estimates body-fat percentage with a legacy U.S. Navy-derived regression using waist, neck, and height, or the Deurenberg equation using BMI, age, and sex.
Reference Limits
Both methods are statistical estimates from body measurements, not current direct body-composition tests. Tape placement, breathing, body shape, sex selection, and differences from the source population can change the result.
When to Confirm Officially
For rapid weight change, hormonal or metabolic disease, pregnancy, an eating disorder, or supervised weight management, do not judge health status or a target weight from this estimate alone. Consult a clinician.
Usage Tips
Measure at the same time and tape position to compare trends
Take neck, waist, and hip measurements under similar conditions, such as in the morning with the same posture and tape placement. Use repeated measurements to compare trends rather than treating one estimate as a professional body-composition test.
What is Body Fat Percentage Calculator?
The Body Fat Percentage Calculator estimates body fat, fat mass, and lean mass from sex, age, height, weight, and circumferences. It compares a legacy U.S. Navy-derived circumference regression with the adult Deurenberg BMI equation and calculates a theoretical target weight assuming lean mass stays constant. Neither result replaces DXA or professional body-composition measurement.
How to Use
- 1Enter sex, age, height, and weight, then choose the preferred units.
- 2Measure and enter neck and waist circumference, plus hip circumference for the female formula.
- 3Choose the circumference or BMI-based method as the primary result.
- 4Enter a target body fat percentage to estimate target weight while holding lean mass constant.
- 5Review both method estimates, the status label, and waist-to-height ratio together.
Comparing circumference and BMI body-fat estimates
Last reviewed: July 10, 2026The equation changes with the selected method
Male circumference = 86.010×log₁₀(waist−neck) − 70.041×log₁₀(height) + 36.76
The circumference equation uses inches; the female version uses waist+hip−neck. The BMI option uses the adult Deurenberg form: 1.2×BMI + 0.23×age − sex adjustment − 5.4.
Example: male, age 30, 175 cm, 80 kg, neck 39 cm, waist 90 cm
- • Circumference method
- • Neck 39 cm and waist 90 cm
- • Target body fat 18%
- 1. circumference estimate = 20.06%
- 2. fat mass = 80×20.06% = 16.05 kg
- 3. lean mass = 80−16.05 = 63.95 kg
- 4. target weight = 63.95÷(1−0.18) = 77.99 kg
Estimated body fat is 20.06%, lean mass 63.95 kg, and theoretical target weight 77.99 kg. Target weight assumes unchanged lean mass.
How to read the result
- Circumference and BMI methods are estimates from different inputs, so a difference between them is not automatically an error.
- Fat mass and lean mass are derived from the selected body-fat estimate, not independently measured values.
- The status label is a general reference and does not replace diagnosis, athletic assessment, or a weight-management prescription.
Conditions that change the result
- The circumference equation is a legacy U.S. Navy-derived regression and varies with measurement technique and population.
- The adult BMI equation reported a standard error of about 4.1 percentage points in the original study and can differ more for an individual or population.
- Target weight assumes lean mass remains constant during weight change, which often does not happen exactly.
Common input mistakes
- Keep the tape level and use the same waist, neck, and breathing landmarks for repeat comparisons.
- Mixing centimeters and inches or changing the unit without converting the value changes the logarithmic result.
- Do not compare a tightly pulled post-workout measurement with a relaxed measurement taken under different conditions.
Reference Knowledge
- ●The circumference option applies a sex-specific logarithmic regression historically used in U.S. Navy body-composition assessment. It is a personal estimate here and should not be treated as the current official military assessment procedure.
- ●The BMI-based estimate uses only BMI, age, and sex adjustment, so it is quick but cannot fully account for individual muscularity or body shape.
- ●Fat mass equals body weight multiplied by body fat percentage, while lean mass equals body weight minus fat mass.
- ●Target weight equals lean mass divided by one minus the target body fat fraction and assumes lean mass does not change.
- ●Waist-to-height ratio divides waist circumference by height and is a supplementary indicator rather than a direct body-fat measurement.
- ●Tape position, breathing, hydration, meals, and recent exercise can change measurements, so repeated checks should use similar conditions.
FAQ
Q.How does the U.S. Navy body fat formula work?
The male equation uses height, waist, and neck measurements, while the female equation also uses hip circumference. Measurements are converted to inches and entered into sex-specific logarithmic equations to provide a practical estimate without specialized equipment.
Q.Why do the Navy and BMI estimates differ?
The Navy method uses circumferences related to body-fat distribution, while the BMI method uses only height, weight, age, and sex. Differences can be larger for people whose muscularity or body shape differs from the population averages behind either formula.
Q.Should I use the target weight as a strict weight-loss goal?
No. The result assumes current lean mass remains unchanged. Water, muscle mass, training status, and measurement error can change during weight loss, so use the number as a comparison reference rather than a diet prescription.
Q.When should I take body circumference measurements?
Measure under similar conditions, such as in the morning with a relaxed posture and consistent hydration. Keep the tape level and lightly touching the skin without compressing it, and use the same anatomical location each time.
Q.Why can this result differ from BIA or DEXA testing?
Circumference formulas estimate from body shape, BIA devices infer composition from electrical resistance, and DEXA uses imaging. Each method has different assumptions and errors, so results may not match. Professional evaluation should take priority for medical decisions.
