BMI Calculator: Body Mass Index & Healthy Weight Range

Body mass index (BMI) is your weight in kilograms divided by your height in meters squared. For adults, a BMI of 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or more is obesity. Someone who is 5 ft 9 in tall and weighs 165 lb has a BMI of 24.4 — a healthy weight — and the healthy range at that height is 125 to 168 lb.

Enter your height and weight above for your BMI, its category, the healthy weight range for your height and how far you are from it. Add an age under 20 and the calculator switches to a BMI-for-age percentile on the CDC growth charts, which is how BMI is read for children and teens.

Worked example

Height: 5 ft 9 inWeight: 165 lb

Your BMI: 24.4 Healthy weight

The healthy weight range at 5 ft 9 in is 125 to 168 lb — the same figures the CDC gives for that height. In metric, 175 cm and 75 kg is a BMI of 24.5.

Open this example in the calculator →

How to use the BMI Calculator

Choose US units (feet, inches and pounds) or metric (centimeters and kilograms).
Enter your height and your weight. Weigh yourself in light clothes, ideally in the morning.
Optionally add your age and sex. Under 20, both are needed for a percentile; for adults they add a body-fat estimate.
Read your BMI, its category and your healthy weight range, with the table of every category at your height below it.

The BMI formula

BMI divides weight by the square of height:

Metric: BMI = weight (kg) ÷ height (m)². For 75 kg and 1.75 m: 75 ÷ (1.75 × 1.75) = 75 ÷ 3.0625 = 24.5.
US units: BMI = 703 × weight (lb) ÷ height (in)². For 165 lb and 5 ft 9 in (69 in): 703 × 165 ÷ 4,761 = 24.4.

The 703 converts pounds and inches into kilograms and meters. This calculator converts with the exact definitions (1 lb = 0.45359237 kg, 1 in = 2.54 cm), so a US and a metric entry of the same body give the same BMI. The answer is rounded to one decimal, and the category is read from that rounded figure — so a BMI shown as 25.0 is always called overweight, never healthy.

Adult BMI categories

For adults aged 20 and over, the World Health Organization and the CDC use the same cut-offs, for men and women alike:

BMI	Category	At 5 ft 9 in
Below 18.5	Underweight	124 lb or less
18.5–24.9	Healthy weight	125–168 lb
25–29.9	Overweight	169–202 lb
30–34.9	Obesity class 1	203–236 lb
35–39.9	Obesity class 2	237–270 lb
40 or more	Obesity class 3 (severe)	271 lb or more

The BMI chart has the same table for every height from 4 ft 10 in to 6 ft 6 in, in pounds and kilograms.

BMI for children and teens

Children's BMI changes as they grow, and differs between boys and girls, so a child's BMI is not read against the adult cut-offs. It is compared with other children of the same age and sex on the CDC growth charts and given as a percentile: below the 5th is underweight, the 5th to below the 85th is healthy, the 85th to below the 95th is overweight, and the 95th or above is obesity. Enter an age under 20 above, or use the BMI calculator for kids and teens for an exact age in years and months.

Asian, Black and other ethnic backgrounds

The same BMI carries a higher risk of type 2 diabetes and heart disease in people of Asian background, and the UK's NICE extends that to people of Middle Eastern, Black African and African-Caribbean background. For these groups NICE uses 23 for overweight and 27.5 for obesity, following a 2004 WHO expert consultation. China, Japan, India and Korea set their own lines. The Asian BMI calculator classifies by each of them.

What BMI does not tell you

BMI is a quick, cheap screen, and at the level of whole populations it tracks body fat and health risk well. For one person it can mislead:

Muscle counts as weight. A muscular athlete can have an "overweight" BMI with little body fat.
It cannot see where fat sits. Fat around the waist and organs is the riskier kind; two people with the same BMI can have very different waists. The waist-to-height ratio catches what BMI misses.
Age and sex change what is under the number. At the same BMI, women carry more fat than men, and older adults more than younger ones — see the BMI calculator for seniors.

That is why the American Medical Association said in 2023 that BMI should not be used alone, and why a 2025 Lancet Diabetes & Endocrinology commission of 58 experts recommended confirming excess fat with a waist measure or a body-fat test before diagnosing obesity (except at a BMI above 40, where excess fat can be assumed).

BMI Prime and the "new BMI"

BMI Prime is your BMI divided by 25, the upper limit of a healthy BMI: 1.00 is the line, and 1.20 means 20% above it. The new BMI, proposed by Oxford mathematician Nick Trefethen, is 1.3 × weight (kg) ÷ height (m)^2.5. Squaring height makes tall people look heavier and short people lighter than they are; the 2.5 power corrects much of that while giving the same answer as ordinary BMI for a person of average height. Both appear in your result.

Where BMI comes from

The Belgian mathematician Adolphe Quetelet noticed in the 1830s that adult weight rises roughly with the square of height. In 1972 the physiologist Ancel Keys tested several height–weight indices against measured body fat, found Quetelet's ratio the best of them, and named it the body mass index. The WHO adopted today's cut-offs in the 1990s.

Frequently asked questions

What is a healthy BMI?

For adults, a BMI of 18.5 to 24.9 is classed as a healthy weight by the WHO and the CDC. For people of Asian background, many guidelines put the top of the healthy range at 22.9. For children and teens, a healthy BMI is between the 5th and the 85th percentile for their age and sex.

How do I calculate my BMI?

Divide your weight in kilograms by your height in meters squared. In US units, multiply your weight in pounds by 703 and divide by your height in inches squared. For example, 165 lb at 5 ft 9 in (69 inches): 703 × 165 ÷ (69 × 69) = 24.4.

What is a healthy weight for my height?

Any weight that gives a BMI of 18.5 to 24.9. At 5 ft 4 in that is 108 to 145 lb; at 5 ft 9 in, 125 to 168 lb; at 6 ft, 137 to 183 lb. Enter your height above, or see the healthy weight calculator and the BMI chart.

Is BMI calculated differently for men and women?

No. The formula and the adult categories are the same for men and women. What differs is the body composition behind the number: at the same BMI, women typically carry more body fat than men. That is why this calculator uses your sex only for the body-fat estimate — and, under 20, to compare a child with others of the same sex.

What BMI is considered obese?

For adults, a BMI of 30 or more is obesity: 30 to 34.9 is class 1, 35 to 39.9 class 2, and 40 or more class 3, sometimes called severe obesity. For people of Asian background, many guidelines use 27.5 instead of 30.

Is BMI accurate for muscular people?

Not on its own. BMI cannot tell muscle from fat, so athletes and people who lift weights can be classed as overweight with little body fat. A waist measurement or a body-fat estimate tells the two apart — try the body fat calculator.

Can I use this BMI calculator for my child?

Yes. Enter an age under 20 along with their sex, and the result becomes a BMI-for-age percentile on the CDC growth charts — the way BMI is meant to be read for children and teens. Adult categories are never used under 20.

Do you store my height and weight?

No. The numbers are used to work out your result and are not saved, and the site sets no tracking cookies. They only go into a link if you choose to share your result.

Sources

For general information only — not a diagnosis or a substitute for advice from a doctor. How we calculate.

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