Can I convert BMI to body fat percentage?

Not exactly — but the Deurenberg formula estimates body fat from BMI, age and sex, which is what the BMI tab of this tool does. It is a statistical estimate, not a direct conversion, so two people with the same BMI can have genuinely different body fat. Treat the output as a rough approximation.

Why do I have a high BMI but low body fat?

BMI only compares your weight to your height; it cannot tell muscle from fat. A muscular person is heavy for their height, so their BMI reads high even though their body fat is low. This is the classic case where a body-fat estimate and BMI disagree — and why athletes are often misclassified by BMI alone.

Which is more accurate, BMI or body fat percentage?

Neither is a laboratory measure. BMI is a quick weight-for-height ratio; a body-fat estimate from tape or the Deurenberg formula is a field approximation with a few-percentage-point margin. Body fat describes composition more directly, but both are estimates — useful for tracking, not for diagnosis.

Compare · Body Fat vs BMI

Body Fat % vs. BMI — What's the Difference?

BMI is weight-for-height; body fat % is how much of your weight is fat. They can disagree. The calculator below opens on the BMI method so you can compute both from the same numbers.

Calculate Body Fat %

Gender

Required: the body-fat formulas use biological sex (male or female) as a variable, so the estimate can’t be calculated without it.

Age (years) (Optional)

Optional — the Navy formula doesn’t use age, but it lets us flag results for under-19s, whose healthy body-fat ranges differ during growth.

Total Weight (kg)

Height

cmft·in

Enter your height in centimeters (e.g., 170 cm)

Neck Circumference (cm)

Waist Circumference (cm)

*This calculator is for informational purposes only. Please consult a healthcare professional before making any health decisions. See our medical disclaimer for more information.

Calculations are powered by the Deurenberg BMI-Based Body Fat Formula (1991), a peer-reviewed, population-validated equation estimating body fat from BMI, age, and sex.

Quick Answer

Two Different Measurements

BMI is your weight relative to your height; body fat percentage is how much of your weight is fat. They answer different questions and can disagree — a muscular person can have a high BMI and low body fat. The calculator above opens on the BMI (Deurenberg) method so you can compute both from the same numbers.

Two Different Questions

BMI asks a simple question: is your weight high or low for your height? It is a ratio — weight in kilograms divided by height in metres squared — and nothing more. Body fat percentage asks a different question: of the weight you carry, how much is fat rather than muscle, bone and water? A number can be reassuring on one scale and unremarkable on the other, because they are not measuring the same thing.

How Each Is Calculated

BMI is weight ÷ height². Body fat, on the BMI tab of this tool, uses the Deurenberg formula, which starts from your BMI and adjusts for age and sex. Work an example: a 30-year-old man of 80 kg and 180 cm has a BMI of about 24.7, and the Deurenberg formula turns that into roughly 20.3% body fat. The two numbers describe the same body from different angles — one a ratio, the other a composition estimate.

Where They Disagree

Because BMI counts every kilogram the same, it treats muscle and fat identically. A lifter with a lot of muscle is heavy for their height and reads high on BMI, even though their body fat is low. The reverse happens too: someone at a normal BMI can carry more fat and less muscle than the number suggests. This is the gap a body-fat estimate is meant to fill.

The Deurenberg Link

The Deurenberg body-fat formula literally begins with BMI, then adds terms for age and sex — so the two are mathematically related, not independent. One consequence: because it was built mainly on Caucasian populations, it under-reads body fat for Asian populations, which is why the calculator flags this and offers the tape method as an alternative.

Which to Use for Tracking

Both are estimates, and which you follow depends on the inputs you have — not on any health ruling. If you can take tape measurements, body fat tracks composition changes that BMI misses; if you only have weight and height, BMI is quick and consistent. Place your weight on the standard scale with the BMI Calculator, estimate the lean half of your body with the Lean Body Mass Calculator, or use both body-fat methods on the full Body Fat Percentage Calculator.

The BMI-to-body-fat estimate uses the Deurenberg formula (Deurenberg et al., 1991), which under-reads body fat for Asian populations. Both BMI and this estimate are approximations, not clinical measurements.

CDC Assessment Guide