What is Body Fat Percentage?
Body fat percentage is the proportion of your total body weight that's made up of fat tissue. Unlike BMI (which just uses height and weight), body fat percentage gives you a clearer picture of your body composition—how much is fat versus muscle, bone, and organs.
Two people can weigh exactly the same but look completely different. A muscular athlete at 180 lbs might have 12% body fat, while someone sedentary at 180 lbs might have 30%. Body fat percentage tells you what your weight is actually made of.
Beyond the Scale
Weight alone doesn't tell you if you're losing fat or muscle
Health Indicator
High body fat correlates with heart disease and diabetes risk
Fitness Progress
Track fat loss while building muscle (not just weight changes)
Realistic Goals
Set targets based on body composition, not just pounds
Why body fat percentage matters more than weight:
- Muscle weighs more than fat — You could get fitter while staying the same weight
- Health risks — Body fat (especially visceral fat) is a better health predictor than weight
- Appearance — Two people at same weight can look very different based on body composition
- Athletic performance — Lower body fat often means better performance in most sports
Body Fat Measurement Methods
There are several ways to measure body fat, ranging from simple estimates to highly accurate lab tests. Here's how they compare:
US Navy Method (This Calculator)
Free & EasyUses body circumference measurements (neck, waist, hips). Accuracy: ±3-4%. Good for tracking changes over time. Just need a tape measure.
Best for: Home tracking, getting started, consistent progress monitoring
Skinfold Calipers
$10-30Pinches skin at various body sites to measure subcutaneous fat. Accuracy: ±3-5% when done correctly. Requires practice and consistency.
Best for: Fitness enthusiasts willing to learn the technique
Bioelectrical Impedance (BIA)
$20-200Smart scales and handheld devices send small electrical current through body. Accuracy varies widely (±5-8%) based on hydration, recent meals, etc.
Best for: Convenience, trend tracking (not absolute numbers)
DEXA Scan
$50-150X-ray scan that measures bone, muscle, and fat separately. Accuracy: ±1-2%. Shows exactly where fat is distributed. Available at medical facilities and some gyms.
Best for: Most accurate option, baseline measurements, medical purposes
Hydrostatic Weighing
$50-100Underwater weighing based on body density. Accuracy: ±1-2%. Was the gold standard before DEXA. Requires special facility.
Best for: Athletes, research settings
Consistency Matters Most
Whatever method you choose, use the same method, same time of day, and same conditions each time. The absolute number matters less than the trend. If you start at 25% and drop to 20%, that's progress regardless of whether the "true" numbers are slightly different.