Useful Utilities

Body Fat Percentage Calculator

Estimate body fat percentage from neck, waist and height measurements (plus bust for women and optional weight), using the published Ideal Body Form equations and the ACE classification table.

Fill in the values and calculate

SexThe published equations differ by sexDefault Male
Height (cm) (cm)*Barefoot height in centimetres — required
Neck (cm) (cm)*Neck girth at the collar — required by the equation
Waist (cm) (cm)*Natural waist girth (navel level) — required
Bust/chest (cm) (cm)Full chest girth — required for women; ignored for menDefault 0
Weight (kg) (kg)Optional — without it the tool solves for ideal weights insteadDefault 0

The form sends itself back to this page — results print below, computed on the server.

No results yet: fill the form above and press Calculate.

About Body Fat Percentage Calculator

This tool estimates body fat percentage with the Ideal Body Form (IBF) equations published in the late 1970s, the only published family that derives body fat from body measurements rather than from weight against a height table. The equations expect inches and stone: for men the raw value is 587.9 minus 3.9614 times neck(inches) plus 4.9106 times waist(inches) plus 23.396 times height(inches) minus 61.92 times weight(stone); for women it is 917.9 minus 4.8807 times neck plus 49.512 times bust/chest plus 28.396 times waist plus 36.234 times height minus 162.46 times weight. The result is divided by 100 to read it as a percentage. You enter centimetres and kilograms; the tool converts to the equation's units internally.

Once the percentage is known, fat mass and lean body mass follow from the body weight directly, and the same equation inverted gives the implied weights for any target body-fat level — which is why the table of target percentages appears even when no weight is entered. Without a weight, the tool solves the equation for the ideal starting weight: the mass at which your measurements would place you at the healthy floor for your sex (10% for men, 16% for women on the published table), a figure the original authors used exactly this way for planning targets.

Limits: the model's own published error is about plus or minus five percentage points, its weight term is linear, and it was validated as a way to track body-fat change at a stable shape over time — not as a way to compare two bodies at very different weights. The ACE category table is a classification aid, not a health standard; calipers and DEXA scans measure something closer to subcutaneous fat and usually disagree by design.

Questions about Body Fat Percentage Calculator

Why does doubling my weight only drop the number a little?

Because the weight term is linear in stone: for men every stone subtracts about 0.62 points (61.92 / 100). That is the published model's behaviour — it tracks small weight changes at fixed measurements honestly and says nothing about large ones.

Can I enter pounds and inches?

The fields are centimetres and kilograms like the other pages on this site; the tool converts to inches and stone internally because that is what the published equations expect.

How does this compare to skinfold tests?

Different by design. This is a whole-body geometry model; calipers measure subcutaneous folds at specific sites. They usually disagree by a few points and each is answering a different question.

What does it give without my weight?

Your measurements still identify the weight at which they would put you at a healthy body-fat level on this model, so the tool shows that ideal starting weight and the full implied-weight table.

Why is my gym tracker's number different?

Trackers infer body fat from heart-rate and power data or BMI relations — an entirely different model. Measurement-based estimates like this one disagree with tracker estimates because they measure different things.

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