Skip to content
EN
Free calculator · no sign-up

BMI calculator

Get your body mass index in a second, along with the WHO category, BMI Prime, the alternative 'new BMI' and the healthy weight range for your height.

Your inputs are saved in this browser and shared across all calculators.

1 Height & weight

Height
cm
ft
in
kg

Lift weights? BMI can't tell muscle from fat, so a muscular person can read "overweight" at a lean body-fat level. Cross-check with the body fat calculator and FFMI.

Body Mass Index

—
BMI–
–
BMI Prime–
New BMI (Trefethen)–
Healthy range for your height–
Difference–

Categories: WHO adult classification. BMI is a screening tool, not a diagnosis, and doesn't apply to children, pregnancy or very muscular people.

Body fat % → Ideal weight

Weight at each BMI category for your height

CategoryBMIWeight range

Embed this calculator

Free to use on your website or blog. Paste this code where you want the calculator to appear.

Free forever, no ads inside the widget. Please keep the credit link below the calculator.

Preview

How BMI is calculated

Adolphe Quetelet devised BMI in the 19th century as a population statistic. It is still around because it is quick, free and correlates reasonably well with body fat across large groups.

BMI = weight(kg) / height(m)² BMI Prime = BMI / 25 New BMI = 1.3 × weight(kg) / height(m)^2.5

Why gym-goers get misclassified

Muscle is dense. A 180 cm man carrying 90 kg at 12% body fat has a BMI near 28, officially "overweight", while being leaner than most of the population. A large analysis of adults (Romero-Corral et al., 2008) found that BMI has good specificity but poor sensitivity for detecting excess body fat, especially in the middle ranges.

Better companions to BMI

  • Waist circumference or waist-to-height ratio, a simple marker of abdominal fat.
  • Body-fat percentage from tape measurements or skinfolds.
  • FFMI, which works like BMI but counts lean mass only.

Frequently asked questions

What is a healthy BMI?

The World Health Organization puts the normal (healthy) adult range at a BMI of 18.5–24.9 kg/m². Overweight is 25–29.9 and obesity is 30 or above. Some Asian populations use lower cut-offs, because health risks start rising at lower BMI values.

Is BMI accurate for people who lift weights?

Often not. BMI only knows your weight and height, so it can't tell muscle from fat, and muscular people regularly land in "overweight" despite low body fat. For lifters, body-fat percentage, waist circumference and FFMI tell you more.

What is BMI Prime?

BMI Prime is your BMI divided by 25, the top of the healthy range. A value of 1.00 sits exactly at the limit, and 0.74–1.00 is the healthy range. Because it's a ratio, you can see at a glance how far above or below the limit you are.

What is the "new BMI"?

Oxford mathematician Nick Trefethen proposed it: 1.3 × weight / height^2.5. His argument is that the classic formula overstates fatness in tall people and understates it in short people. It is not an official clinical standard.

Sources & further reading

  1. World Health Organization (2000). Obesity: preventing and managing the global epidemic. Report of a WHO consultation (WHO Technical Report Series 894)
  2. WHO Expert Consultation (2004). Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies . Lancet 363(9403):157–163 · doi:10.1016/S0140-6736(03)15268-3
  3. Romero-Corral A, et al. (2008). Accuracy of body mass index in diagnosing obesity in the adult general population . Int J Obes 32(6):959–966 · doi:10.1038/ijo.2008.11