BMI Calculator
This free BMI calculator works out your Body Mass Index for adults from your height and weight, in metric or imperial units, and shows the WHO category next to it. The result updates as you type, there is no Calculate button, and nothing you enter is uploaded or saved. No sign-up needed.
How to calculate BMI in kg and cm or pounds and feet
Pick Metric to enter your height in centimetres and your weight in kilograms, or Imperial to enter feet and inches for height and pounds for weight. Each system keeps its own numbers, so switching back and forth never wipes what you typed. Your BMI appears at the top as soon as both height and weight are filled in, rounded to one decimal place, with its category underneath.
BMI formula: metric and imperial
BMI is your weight in kilograms divided by your height in metres, squared. In imperial units the calculator first converts: pounds times 0.453592 gives kilograms, and total inches (feet times 12, plus inches) times 0.0254 gives metres. Then it applies the same formula.
| Height | Weight | Working | BMI |
|---|---|---|---|
| 170 cm | 70 kg | 70 ÷ 1.70² | 24.2 |
| 5 ft 7 in | 155 lb | 70.3 ÷ 1.70² | 24.3 |
WHO BMI categories for adults
The category comes from the rounded BMI, using the World Health Organization's adult bands.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obese |
What a BMI number does and doesn't tell you
BMI is a quick screening number built from two measurements. It does not measure body fat, muscle, age or where weight is carried, so it can misjudge very muscular people, and it is not a diagnosis. The bands above are for adults; children and teenagers use age-and-sex percentile charts that this calculator does not cover. For what a number means for you, ask a doctor.
Frequently Asked Questions
Is the BMI calculation the same for men and women?
Yes. For adults the formula and the WHO categories are the same for men and women: weight in kilograms divided by height in metres squared. This calculator does not ask for age or sex. Children and teenagers are assessed with age-and-sex percentile charts instead, which this calculator does not do.
What are the WHO BMI categories for adults?
The WHO adult categories are Underweight below 18.5, Normal weight from 18.5 to 24.9, Overweight from 25.0 to 29.9, and Obese at 30.0 and above. The calculator rounds your result to one decimal place first and then picks the category, so the number and the label on screen always agree.
How do I calculate BMI in pounds and inches?
Switch to Imperial and enter your height as feet and inches in the two height boxes, then your weight in pounds. The calculator converts pounds to kilograms (multiply by 0.453592) and total inches to metres (multiply by 0.0254), then divides weight by height squared. For example, 155 lb at 5 ft 7 in works out to a BMI of 24.3.
What is the BMI formula in kg and cm?
BMI equals weight in kilograms divided by height in metres squared. If your height is in centimetres, divide it by 100 first. For example, 70 kg at 170 cm is 70 divided by 1.7 squared, which is 70 divided by 2.89, giving a BMI of 24.2.
What is a healthy BMI range?
The WHO calls a BMI from 18.5 to 24.9 the Normal weight range for adults. BMI is only a screening number based on height and weight, so it is not a verdict on anyone's health. A doctor can tell you what a given number means for you.
Is BMI accurate for muscular people or athletes?
Not always. BMI uses only height and weight, so it cannot tell muscle from fat, and a very muscular person can land in the Overweight or Obese range without carrying excess fat. Treat it as a quick screening number, not a diagnosis, and ask a doctor if you want a fuller picture.
Does this BMI calculator work for children or teens?
No. It applies the adult WHO categories only. Children and teenagers need age-and-sex percentile growth charts, so for anyone under 18 check with a paediatrician or a growth-chart source rather than this result.
Is my height and weight sent anywhere?
No. The calculation runs entirely in your browser, and nothing you enter is uploaded or saved. There is no account and no Calculate button; the result updates as you type.
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