What Is BMI?
Body Mass Index (BMI) is a numerical value derived from a person's height and weight. Developed in the 1830s by mathematician Adolphe Quetelet, it became a widely used clinical tool following endorsement by the World Health Organization (WHO). BMI provides a quick and inexpensive way to screen for weight categories that may lead to health problems.
How Is BMI Calculated?
The formula is simple:
BMI = Weight (kg) ÷ Height² (m)
For example, a person who is 1.70 m tall and weighs 70 kg has a BMI of 70 ÷ (1.70 × 1.70) = 24.2 — within the normal range.
Limitations of BMI
BMI is useful as a population-level screening tool, but has well-documented limitations for individuals:
- Athletes & bodybuilders — high muscle mass inflates BMI without excess fat.
- Elderly individuals — may carry excess fat at lower BMIs due to muscle loss.
- Ethnicity — some studies suggest lower BMI thresholds for Asian populations.
- Pregnancy — BMI is not an appropriate measure during pregnancy.
- Children — BMI-for-age percentiles should be used instead.
Frequently Asked Questions
Is this BMI calculator accurate? ▾
Yes. It uses the standard WHO formula: weight in kilograms divided by height in metres squared. Results are identical to those produced by clinical screening tools.
What is the ideal BMI for adults? ▾
The WHO defines a healthy BMI as 18.5–24.9 for adults. A BMI below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese.
Is BMI a medical diagnosis? ▾
No. BMI is a screening tool only. A high or low BMI does not diagnose any health condition. Always consult a qualified medical professional for a full health assessment.
Can I use this calculator on mobile? ▾
Absolutely. The calculator is fully responsive and works on all screen sizes including smartphones, tablets, and desktops.
How do I calculate BMI in imperial units (pounds and inches)? ▾
Switch to "Imperial" mode above. The calculator will accept weight in pounds and height in inches, then convert automatically using the formula: BMI = (weight in lbs × 703) ÷ height² (in²).