BMI Calculator

Body Mass Index (BMI) is the world's most widely used first-pass health measure: a single number, calculated from your height and weight, that places you in one of four broad ranges. Doctors use it as a screening tool, insurers use it in underwriting, and it is quoted everywhere from fitness apps to school reports. This free calculator works in metric or imperial units and explains your result in plain language — including the important caveats, because BMI is a starting point for a conversation about health, not a diagnosis.

Who it is for: adults who want a quick, standardised reference number. Example: you are starting a fitness programme and want a baseline. Enter 82 kg and 176 cm and you get a BMI of about 26.5 — in the "overweight" range — which tells you the direction to work in, while the notes below explain why a muscular person can land there too.

Health disclaimer: BMI is a general screening estimate, not a medical diagnosis. It does not distinguish fat from muscle and is not designed for children, pregnant people, or elite athletes. If you have concerns about your weight or health, please speak to a qualified health professional. See our full Disclaimer.

How to Use the BMI Calculator

  1. Choose metric or imperial units.
  2. Enter your weight and height as accurately as you can — ideally measured in the morning, without shoes.
  3. Click Calculate BMI. Your result uses the World Health Organization formula: weight in kilograms divided by height in metres squared.
  4. Compare your number with the standard adult ranges: below 18.5 underweight; 18.5–24.9 healthy weight; 25–29.9 overweight; 30 and above obese.

Frequently Asked Questions

What is a healthy BMI?

For most adults, the World Health Organization's healthy range is 18.5 to 24.9. It is a range, not a target — a BMI anywhere inside it is considered healthy, and small movements within it are not meaningful.

Why can athletes have a "high" BMI?

BMI uses total weight and cannot tell muscle from fat. A muscular athlete can score in the overweight or even obese range while having low body fat. Waist measurement and professional assessment give a fuller picture. Our article How BMI Works — and Where It Misleads explains the limits in depth.

Is this BMI calculator suitable for children?

No. Children and teenagers need age- and sex-specific BMI percentile charts, because healthy body composition changes as they grow. Ask a paediatrician or school nurse for a child-specific assessment.

How often should I check my BMI?

For general tracking, once every month or two under similar conditions is plenty. Day-to-day weight naturally fluctuates by a kilogram or more with hydration and meals, so frequent checks mostly measure noise.