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A body fat calculator estimates what percentage of your body weight is actually fat, using simple tape-measure inputs like your waist, neck, and (for women) hip measurements. This is the US Navy method — no calipers, no scans, just a measuring tape and a few numbers. It gives a more useful picture than BMI alone because two people at the same weight can have very different body fat percentages.
BMI treats a bodybuilder and someone carrying extra fat the same way if their weight and height match — which obviously isn't fair or accurate. This tool exists for people who want a better sense of their actual body composition without paying for a DEXA scan or expensive gym assessment. Just grab a tape measure and you're set.
The Navy method uses circumference measurements plugged into a logarithmic formula, which correlates reasonably well with more expensive methods like hydrostatic weighing. It won't be as precise as a DEXA scan, but for tracking progress month to month, it's a solid, repeatable way to see if your body composition is actually changing — even when the scale isn't moving much.
It's typically within 3-4% of more expensive methods like DEXA scans, which makes it good enough for tracking progress over time.
For men, roughly 10-20% is considered fit/healthy. For women, it's usually 18-28%, though this varies by age and activity level.
The neck measurement helps account for upper body fat distribution and improves the accuracy of the formula compared to waist alone.
Not exactly — a DEXA scan is more precise, but this method is free, fast, and good enough for most people tracking changes over weeks or months.
Yes, measuring first thing in the morning before eating or drinking gives the most consistent results day to day.