Body Fat Calculator
The scale is a liar. Find out what your weight is actually made of with the military-grade US Navy Method.
Measurements (US Navy Method)
Body Fat Percentage
Enter Measurements
Your Body Fat Percentage is the only metric that truly defines "fitness." It distinguishes between 200lbs of muscle (Bodybuilder) and 200lbs of fat (Obese), which BMI treats as identical.
Not all fat is bad. You need Essential Fat (3% for men, 12% for women) to survive. It protects organs and regulates hormones. Everything above that is Storage Fat—this is the energy reserve we try to reduce.
The "Skinny Fat" Trap
Many people diet strictly using a scale. They lose weight, but they look "soft." This is caused by losing muscle along with fat.
The number on the scale goes down. This could be water, glycogen, muscle, or fat. Often results in a slower metabolism.
The percentage of body fat decreases while muscle is maintained or built. This results in a "toned" look and a faster metabolism.
Stop trying to lose weight. Start trying to lose fat.
Body Recomposition Strategy
How to lose fat without losing muscle
To improve your body fat percentage, you need to convince your body that muscle is *essential* for survival.
- 1. Lift Heavy:Resistance training signals to your body: "We need this muscle to lift these heavy things. Do not burn it for fuel."
- 2. Eat High Protein:Common diets fail here. If you cut calories but don't eat enough protein (1.6g per measured kg of bodyweight), your body will cannibalize its own muscle tissue.
- 3. Moderate Deficit:Don't starve. A deficit of 500 calories/day is enough to burn fat while sparing muscle.
The Math: US Navy Circumference Method
Developed by the Naval Health Research Center, this formula uses body geometry to estimate density. It relies on the gap between your waist size (adipose storage) and your height/neck size (skeletal/muscle frame).
Men
495 / (1.0324 - 0.19077(log10(Waist - Neck)) + 0.15456(log10(Height))) - 450Women
495 / (1.29579 - 0.35004(log10(Waist + Hip - Neck)) + 0.22100(log10(Height))) - 450*Waist, Neck, and Hip in cm. Height in cm.
Calculation Example
Profile: Male, 178cm tall.
- Neck: 38cm
- Waist: 85cm
- Math: log10(85-38) and log10(178)...
- Result: ~15.2% Body Fat
Context: This falls into the "Fitness" category, showing visible muscle definition and good metabolic health.
Visualizing Progress
Comparison of 3 individuals at 200 lbs (Male).
Sedentary
Body Fat: 35%
Lean Mass: 130 lbs
Fat Mass: 70 lbs
Low metabolism, high risk of chronic disease.
Weekend Warrior
Body Fat: 20%
Lean Mass: 160 lbs
Fat Mass: 40 lbs
Healthy baseline. Good metabolic flexibility.
Bodybuilder
Body Fat: 10%
Lean Mass: 180 lbs
Fat Mass: 20 lbs
Elite conditioning. High calorie burn at rest.
ACE Body Fat Standards
Official ranges from the American Council on Exercise.
| Category | Women | Men | Notes |
|---|---|---|---|
| Essential Fat | 10-13% | 2-5% | Minimum required for life. |
| Athletes | 14-20% | 6-13% | High muscle definition. |
| Fitness | 21-24% | 14-17% | Healthy, visibly fit. |
| Average | 25-31% | 18-24% | Normal population average. |
| Obese | 32%+ | 25%+ | High health risk. |
Related Tools
Why does the Navy Method use neck size?
It seems odd, but neck circumference is a strong proxy for upper body fat distribution and, conversely, muscle mass. A thick neck often indicates higher muscle mass (lowering estimated body fat), while a thick waist indicates visceral fat (raising it).
Is this as accurate as a DEXA scan?
No. DEXA (X-ray) is the Gold Standard. However, the US Navy Method is widely considered the most accurate *home* method—often beating expensive 'Smart Scales' that use bioelectrical impedance (which fluctuates wildly with hydration).
Can I target belly fat with situps?
No. 'Spot reduction' is a persistent fitness myth. You cannot tell your body *where* to burn fat from. Situps build abdominal muscle, but they won't burn the fat covering them. Only a caloric deficit can do that.
What is a healthy body fat percentage?
For men, 10-20% is considered healthy/athletic. For women, 18-28% is the equivalent range. Women naturally require more essential fat for hormonal function and reproductive health.
I lost weight but my body fat % went up. Why?
This happens if you lose muscle faster than you lose fat (common with crash diets or no exercise). If you lose 10lbs of muscle and 0lbs of fat, your total weight drops, but your *percentage* of fat increases. This is why resistance training is crucial.
Composition Terms
Lean Body Mass (LBM)
Everything in your body that isn't fat: Organs, bones, blood, water, and muscle. This is the metabolic engine of your body.
Adipose Tissue
The scientific name for body fat. It serves as an energy reserve, insulation, and hormonal regulator.
Subcutaneous Fat
Fat stored directly under the skin. Pinchable fat. Less dangerous than visceral fat but harder to lose.
Bioelectrical Impedance
The technology used by handheld fat monitors and smart scales. It sends a weak electric current through the body. It is often inaccurate because hydration levels affect conductivity.
About This Calculator
This tool uses the US Navy Circumference Method (Equation 10-1 from the Naval Health Research Center). It is widely regarded as the most accurate anthropometric method for estimating body composition outside of a laboratory setting.