Glossary
Body Fat Percentage
Updated April 3, 2026
Body fat percentage estimates how much of your total body weight is fat tissue. It can be useful, but only if you treat it as an estimate with method-specific error, not as a perfectly precise statement about your body.
Use fat-free mass as a companion value when you want to separate composition change from body-weight noise.
Method confidence bands
Method choice sets the margin of error, so interpretation should always include confidence limits.
| Method | Typical confidence band | Best use window | Primary artifact |
|---|---|---|---|
| DEXA | ±1 to 3 percentage points | periodic baseline and body composition reviews | hydration shifts and device software updates |
| Bioimpedance | ±2 to 5 percentage points | frequent trend checks | hydration and electrolyte swings |
| Skinfold calipers | ±3 to 5 percentage points with expert operator | low-budget recurring tracking | site consistency and tester technique |
| Scale model estimates | ±3 to 8 percentage points | daily direction checks only | timing, hydration, and activity residue |
What creates false movement
Weekly pattern and timing distortions can look like fat changes.
| Distortion source | Typical direction | How to control |
|---|---|---|
| Morning hydration and salt | transient rise in one side of trend | standardize morning weigh-ins and fluids |
| Exercise within 24 hours | transient drop from glycogen and water shifts | avoid hard sessions before comparison scans |
| Meal timing and sodium spikes | temporary increase in water compartments | compare same precondition windows |
| Heat exposure and sleep debt | unstable baseline impedance | delay interpretation until recovery stabilizes |
Noise-floor rules and interpretation
Do not act on minor movement. Treat a swing as noise unless it exceeds method-specific floor and confirms across windows.
| Method | Noise floor to trust | Decision rule |
|---|---|---|
| DEXA | ≥2 points over two measurements | treat as real shift if repeated |
| Bioimpedance | ≥3 points over three daily points | only adjust if hydration and sleep are stable |
| Skinfold calipers | ≥2 points by same assessor | accept if technique and site are consistent |
| Scale estimate | ≥3 to 4 points over 3 to 4 weeks | use trend only with other methods |
Reporting rhythm
For coaching use, keep one method and one regular check-in window. If different methods disagree, prioritize the trend within the same method before you react to the absolute number. Then compare that trend against body weight, waist, training performance, and recovery.
Reference bands
| Category | Men | Women |
|---|---|---|
| Essential | ~2%–5% | ~10%–13% |
| Athletes | 6%–13% | 14%–20% |
| Fitness | 14%–17% | 21%–24% |
| Average | 18%–24% | 25%–31% |
| Higher | ≥25% | ≥32% |
Use the same method each time if you want the number to mean anything across months. For the full method-specific decision framework, read DEXA Scan for Body Composition: How Accurate Is It for Fat Loss and Muscle Gain?.