Body fat calculator
Estimate body fat percentage from a tape measure using the US Navy circumference method, and get fat mass and lean mass alongside it. No calipers, no scan, three measurements.
Measure at the same time of day, in the same state, every time. The method is more useful for tracking a direction than for pinning down an absolute number.
- Fat mass
- 12.5 kg
- Lean mass
- 67.5 kg
- Descriptive band
- Fitness
An estimate from a published formula, not a measurement. Use it as a consistent yardstick for tracking change.
What the bands mean
These are descriptive categories in common use, not clinical thresholds. Athletic populations routinely sit outside them in both directions.
| Band | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletic | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Above average | 25%+ | 32%+ |
How to take the measurements
- Neck: just below the larynx, tape sloping very slightly downward at the front. Do not flex.
- Waist: men at the navel; women at the narrowest point. Tape snug, not tight, at the end of a normal exhale.
- Hips (women only): at the widest point, feet together.
Consistency beats precision. Measuring the same way every time makes the change meaningful even if the absolute number is a few points off.
What the method can and cannot do
The Navy equation predicts body fat from circumferences and height, using the fact that fat distributes in reasonably predictable places. Against a DEXA scan it typically lands within about three to four percentage points for average builds, and drifts further for very lean or very muscular people.
It reads high on a thick-waisted lifter with a large amount of abdominal muscle, and low on someone slim with little muscle. Neither error is a fault in the tape; it is a method that cannot tell muscle from fat under it.
Comparing methods, briefly
DEXA is the practical reference standard and still varies between machines. Hydrostatic weighing and air displacement are close behind. Skinfold calipers are good in trained hands and poor otherwise. Bioimpedance scales are heavily affected by hydration and can move several points between morning and evening.
The important rule is not to mix them. A number from a scan in January and a tape measurement in March is not a trend, it is two different methods disagreeing.
The number is not the goal
Body fat percentage moves for reasons that have nothing to do with fat: a gain in lean mass lowers it at identical fat mass. That is why fat mass and lean mass are shown separately above. Watching those two move in opposite directions is far more informative than watching the percentage alone.
Questions people ask
How accurate is the Navy body fat method?
Typically within three to four percentage points of a DEXA scan for average builds, with larger errors at the extremes. It is a reasonable tracking tool and a poor absolute measurement, which is true of nearly every accessible method.
Why did my body fat go up when my weight went down?
Usually a measurement issue rather than a real change: waist circumference varies with bloating, hydration and time of day. Measure first thing in the morning, fasted, and compare four-week averages rather than single readings.
What body fat percentage should I aim for?
For general health, roughly 10 to 20% for men and 18 to 28% for women covers a wide healthy range. Lower is not automatically better: very low body fat carries real hormonal and performance costs, particularly for women.
Are body fat scales any good?
For a single reading, not really. They estimate from electrical impedance, which swings with hydration, food and skin temperature. Used consistently at the same time of day they can show a direction, which is about all they should be asked for.
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