BMI Calculator

In 1832, the Belgian statistician Adolphe Quetelet was studying population averages (height, weight, chest size, even arrest records) when he noticed that adult weight scaled roughly with the square of height rather than with height alone. He published the ratio as the "Quetelet Index" and moved on. Nobody used it medically for over a century. In 1972, Ancel Keys revived the formula, renamed it Body Mass Index, and showed it correlated with body-fat percentage at a population level. The World Health Organization adopted the four-category scale in 1995. The math has not changed: divide your weight in kilograms by the square of your height in meters. What has accumulated is the context, including the important caveat that BMI was always a population-level statistic rather than a per-individual diagnostic. This calculator gives you your BMI, your WHO category, and the healthy weight range for your height. The related concepts section explains what BMI actually measures and what it misses.

1. 1Enter your weight in kilograms. To convert from pounds, divide by 2.2046.
2. 2Enter your height in centimeters. To convert from inches, multiply by 2.54.
3. 3The calculator converts height from centimeters to meters by dividing by one hundred.
4. 4It then computes weight divided by the square of height in meters.
5. 5The result maps to one of four WHO categories: underweight, normal weight, overweight, or obese.
6. 6It also computes the healthy weight range for your height (the weights that would give you a BMI between 18.5 and 24.9).

• Routine health screening: BMI is the most common first-pass weight assessment in primary care. A doctor will calculate it during an annual physical to flag the need for a more detailed body-composition check or lifestyle conversation. The two-minute calculation is far cheaper than a DEXA scan, even if it is also far less precise.
• Tracking weight-loss or fitness progress: Plug in your weight monthly and watch the BMI trend rather than the daily scale number. Over months, the trend matters more than the noise. For active people, pair BMI with waist circumference. Gaining muscle while losing fat can leave BMI flat even when body composition improves.
• Insurance and corporate wellness scoring: Many life-insurance underwriters and corporate-wellness incentive programs use BMI brackets as part of their risk-rating math. Knowing where you fall on the WHO scale lets you anticipate questions or premiums before they arrive.
• Public-health surveillance: Population-level BMI distributions are tracked by the CDC, WHO, and national statistics offices to monitor obesity prevalence. The same formula you use here is the input to those datasets, applied at scale.

• Treating BMI as a diagnosis: BMI is a screening number, not a diagnosis. Use it to decide whether a deeper conversation with a doctor is worthwhile, not to label yourself.
• Comparing BMI across very different ages or builds: A 25-year-old athlete and a 70-year-old retiree at BMI 26 are in very different health situations. BMI brackets do not adjust for age, muscle mass, or frame size.
• Mixing units: The calculator expects kilograms and centimeters. If you enter pounds in the weight field, your BMI will appear inflated by roughly 2.2×. Convert first.

• Track waist circumference alongside BMI: A tape measure is the cheapest extra signal you can add. BMI tells you relative weight; waist circumference tells you where you carry it. Where you carry fat matters as much as how much you carry.
• Re-check monthly, not daily: Body weight fluctuates by 1–2% day to day from water, food, and glycogen. Weighing yourself once a week or once a month and tracking the trend filters that noise.
• Use the healthy weight range as a target band, not a single number: The 6–10 kg span between BMI 18.5 and 24.9 for most adult heights is a band you can sit anywhere within. There is no medical reason to optimize for the middle.