WeightLogBody fat calculator
Estimate your body fat percentage from a few tape measurements. You'll also see your fat mass, lean mass and the healthy range for your age and sex.
Body fat
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–- Fat mass
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- Lean mass
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For adults aged 20 and over. A tape measure estimate can be a few percentage points off, so use it to follow change over time rather than as an exact figure.
How to measure
- Use a flexible tape on bare skin. Keep it snug but not tight, and stand relaxed without pulling your stomach in.
- Neck: just below the Adam's apple, with the tape sloping slightly down at the front.
- Waist: men at the level of the belly button, women at the narrowest point.
- Hips (women only): at the widest part of the hips and buttocks.
- Measure two or three times and use the average.
How it's calculated
This is the U.S. Navy circumference method, the one the WeightLog app uses. With all measurements in centimeters:
Men: 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Women: 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hips − neck) + 0.221 × log₁₀(height)) − 450
Fat mass is your weight times that percentage, and lean mass is the rest.
Source: Hodgdon and Beckett, U.S. Naval Health Research Center, reports 84-11 (men) and 84-29 (women), 1984. The last step, 495 ÷ density − 450, is the Siri equation (1961): it turns body density into a fat percentage.
Ranges by age and sex
The calculator compares your result with these adult ranges, the same as in the app.
| Group | Low | Healthy | High | Very high |
|---|---|---|---|---|
| Women 20–40 | < 21% | 21–33% | 33–39% | 39%+ |
| Women 41–60 | < 23% | 23–35% | 35–40% | 40%+ |
| Women 61+ | < 24% | 24–36% | 36–42% | 42%+ |
| Men 20–40 | < 8% | 8–19% | 19–25% | 25%+ |
| Men 41–60 | < 11% | 11–22% | 22–27% | 27%+ |
| Men 61+ | < 13% | 13–25% | 25–30% | 30%+ |
Body fat next to every weigh-in
Each weigh-in in WeightLog carries a body fat estimate. By default it's calculated from your BMI, and you can replace it with your own number or a tape measure calculation like this one.
More calculators
BMI
Your body mass index and the healthy weight range for your height.
Daily calories
Your basal metabolic rate and the calories to maintain, lose or gain weight.
Calories burned
The energy you use in 25 activities, from walking and running to cycling and swimming.
Heart rate zones
Your estimated maximum heart rate and five training zones in beats per minute.
Waist-to-height ratio
How your waist compares with your height: a quick check of fat around the middle.
