What body fat percentage is good?

It depends on sport, sex and life stage. Very low values are not automatically better and can disrupt hormones and immunity.

Why does my scale at home disagree?

Body fat scales measure electrical resistance and react strongly to hydration. The number fluctuates daily without real change.

Will losing weight make me faster?

Up to a point yes, beyond it no. Go too far and you lose power, recovery and health.

BMI & Body Fat

Calculate BMI and body fat percentage

Weight (kg)

Height (cm)

Age

Sex

Body fat method

BMI23.7 — Normal weight

Body fat (Deurenberg)19.1 %

What the calculator shows

Two numbers: BMI, which only combines weight and height, and an estimate of body fat percentage from circumference measurements.

For athletes, body fat percentage is the more meaningful figure because it distinguishes muscle from fat — BMI does not.

How it is calculated

BMI = weight in kg / (height in m)². Body fat by Deurenberg = 1.2 × BMI + 0.23 × age − 10.8 × sex (1 = male, 0 = female) − 5.4. Body fat by the US Navy method: men 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76, women 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387, all measurements in cm.

Deurenberg derives fat from BMI, age and sex only and runs high for muscular athletes; the Navy method uses circumferences and does better there.

Example: 70 kg, 175 cm, male, 30 years. BMI = 70 / 1.75² = 70 / 3.06 = 22.9. Deurenberg = 1.2 × 22.9 + 0.23 × 30 − 10.8 − 5.4 = 27.5 + 6.9 − 16.2 = 18.2 %. Navy with an 85 cm waist and 38 cm neck: 86.010 × log10(47) − 70.041 × log10(175) + 36.76 = 23.5 %.

BMI classes: under 18.5 underweight, up to 25 normal, up to 30 overweight, above that obesity — a rough guide for endurance athletes, not a diagnosis.

To calculate body fat consistently, measure in the morning without tensing your abdomen and compare only against your own earlier readings.

Please use with judgement

BMI routinely classifies muscular people as overweight when they are not. For athletes it is often simply the wrong tool.

The body fat figure is an estimate too. Treat it as a rough reference and watch the trend rather than chasing a target number.

Frequently asked questions

What body fat percentage is good?: It depends on sport, sex and life stage. Very low values are not automatically better and can disrupt hormones and immunity.
Why does my scale at home disagree?: Body fat scales measure electrical resistance and react strongly to hydration. The number fluctuates daily without real change.
Will losing weight make me faster?: Up to a point yes, beyond it no. Go too far and you lose power, recovery and health.