Calculation results
Body fat percentage:
Body fat category:
Body fat mass:
Lean body mass:
Ideal body fat for age:
Body Fat Calculator
What this calculator measures
Knowing your body fat percentage tells you how much of your weight is fat versus lean tissue, a far better health signal than BMI alone. This tool estimates it with the US Navy tape method, which needs nothing more than a flexible tape and a scale.
Gym members, military applicants, and anyone cutting or bulking genuinely benefit from tracking it. Weight can stay flat while fat drops and muscle rises, and body fat percentage exposes that change when the bathroom scale hides it.
The Navy formula in practice
The estimate comes from Hodgdon and Beckett’s 1984 Navy research: circumference ratios predict body density, and the Siri equation turns density into a fat percentage. Men log Weight:, Height:, Neck:, and Waist:; women also add their hip measurement. In metric terms, a man’s result equals 495 divided by (1.0324 minus 0.19077 times log10 of the waist minus neck gap, plus 0.15456 times log10 of height), then 450 is subtracted.
Worked example: a male 180 cm tall with a 38 cm Neck: and an 85 cm Waist: has a waist minus neck gap of 47 cm. Feeding those numbers through the formula leaves him at roughly 15 to 16 percent body fat, comfortably inside the fit range for adult men.
How to take tape measurements
Choose Metric or Imperial, enter Age:, Weight:, Height:, then measure the Neck: just below the larynx and the Waist: at the navel for men or at the natural waist, adding the Hip: at its widest point for women. Keep the tape level and snug but never pinching the skin.
For accuracy, average three readings and remember the tool estimates a range, not an exact truth. Essential fat sits at about 2 to 5 percent for men and 10 to 13 percent for women, so anything near those floors is territory for medical supervision.
Frequently Asked Questions
What is a healthy body fat percentage?
Fitness ranges run from about 6 to 17 percent for men and 14 to 24 percent for women; above 25 and 32 percent respectively counts as obese. Essential fat is just 2 to 5 percent for men and 10 to 13 percent for women.
How accurate is the Navy tape method?
Studies put its error around 3 to 4 percent compared with lab methods like DEXA, so a reading of 20 percent could really be 17 to 23 percent. It is best used for tracking trends in the same way each time.
Why does the neck measurement matter?
The neck is included because a thicker neck adds lean mass rather than fat, so subtracting it from the waist offsets padding elsewhere. A 1 cm measurement slip can shift the result by nearly 1 percent.
Does age change the body fat result?
The tape formula itself ignores age, but interpreted standards shift with it, since healthy fat percentage rises modestly each decade after about age 30. Older adults should compare against age-adjusted charts.
Can body fat be too low?
Yes, dropping below essential fat, which is 2 to 5 percent for men and 10 to 13 percent for women, impairs hormone production and immunity. Such levels normally appear only in controlled athletic or medical settings.