BMI Calculator
Calculate adult BMI or CDC BMI-for-age percentile for teens aged 12 to 19, with category ranges, formulas, limitations, and browser-only privacy.
Results
How to calculate BMI: the body mass index formula
BMI stands for body mass index, and it is weight measured against height squared. The BMI formula in metric units is weight in kilograms divided by height in metres squared. In U.S. customary units the same BMI equation is weight in pounds divided by height in inches squared, multiplied by 703. Both express the same measure, so the unit selector changes the figures you type, not the result you get.
Worked through: someone 1.75 m tall weighing 70 kg has a BMI of 70 divided by 1.75 squared, which is 22.9. Someone 5 ft 9 in weighing 154 lb has a BMI of 154 divided by 69 squared, multiplied by 703, which is 22.7. Set the unit selector to metric to use this as a BMI calculator in kg and centimetres, or to U.S. customary for feet, inches and pounds.
Classification always uses the unrounded value. BMI is rounded to one decimal for display only, so a figure shown as 25.0 is never placed in a band the exact value does not reach.
Using the BMI calculator online, in kg or in pounds
This is a free online BMI (body mass index) calculator. It runs in the browser, needs no account, and sends nothing to a server. Set the unit selector to metric to use it as a BMI calculator in kg, entering height in centimetres and weight in kilograms, or to U.S. customary to enter feet, inches and pounds. Either way the body mass index calculator works from the same underlying ratio, so both routes give one answer.
Calculating body mass index by hand is the arithmetic in the section above: divide weight in kilograms by height in metres squared. For adults a BMI calculator with age behaves no differently from one without, because age selects the adult bands from 20 onward and changes nothing about the figure. It only alters the answer between 12 and 19, where it selects a growth reference.
The measure travels under several names. BMI is short for body mass index, and corporal mass index is what the Spanish and Portuguese name for it becomes when translated word for word. All of them name the same ratio of weight to height squared, and this page calculates that one figure.
The adult categories below are the CDC bands, and this page applies them wherever the reader is, so using it as a BMI calculator in India, the United Kingdom or the United States returns the same category for the same figure. If your own health service works to different thresholds, follow the advice it gives you.
BMI chart: adult body mass index categories
The body mass index chart below applies from age 20. The BMI chart below is a single scale for everyone in that range: adult body mass index uses neither a different formula nor a different threshold by sex, so one chart serves men and women.
| Category | BMI |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to below 25 |
| Overweight | 25 to below 30 |
| Obesity, class 1 | 30 to below 35 |
| Obesity, class 2 | 35 to below 40 |
| Obesity, class 3 | 40 and above |
A BMI table, a BMI scale and a BMI chart are the same object under three names, and the table above is it. It also serves as a healthy body weight calculator: alongside the category, the page shows the healthy body weight range a BMI of 18.5 to 24.9 corresponds to at the height entered, and the smallest change that would reach it.
BMI calculator for men and women
A female BMI calculator and a male BMI calculator are usually expected to produce different numbers. For adults there is no difference to produce: the body mass index formula and the six thresholds in the chart above are identical for men and women, so this one page serves as a BMI calculator for men and a BMI calculator for women without changing anything between them.
Sex is asked because it does change the answer between the ages of 12 and 19, where BMI is read against a CDC growth reference specific to sex and to month of age. Age is asked for the same reason, which is all a BMI calculator with age is doing: below 20 it selects the growth reference, and from 20 it selects the adult bands and then does not affect the figure.
BMI does not measure body fat directly and cannot separate muscle from fat. Average body composition differs between men and women at the same BMI, which is one of the reasons BMI is a screening measure rather than a diagnosis, for either.
BMI for ages 12 to 19
While a person is still growing, the same BMI means different things at different ages. Between 12 and 19 the calculator compares BMI against CDC BMI-for-age growth references for that sex and month of age, and reports a percentile, the percentage of the 95th percentile, and the thresholds that apply at that exact age.
Below the 5th percentile is underweight; the 5th to below the 85th is a healthy weight; the 85th to below the 95th is overweight; the 95th and above is obesity; severe obesity begins at 120 per cent of the 95th percentile, or a BMI of 35, whichever is reached first.
This is why ages 12 to 19 are asked for completed months as well as years, and why the reference is chosen by sex. A birth date is never requested, and no weight target is produced for this age group.
What BMI does not tell you
BMI is a screening measure, not a diagnosis and not a substitute for professional medical advice. It does not measure body fat directly and cannot separate muscle from fat, so it can read high for people who are very muscular. It is not a suitable measure during pregnancy.
For ages 12 through 19 it is one growth screening measure among several. A clinician considers growth over time, medical history, health behaviours, examination findings and laboratory findings.
Sources
- CDC: adult BMI categories
- CDC: child and teen BMI
- CDC: 2022 Extended BMI-for-age data files
- NHS: body mass index
Sources reviewed 25 August 2026.
Frequently asked questions
Is BMI a diagnosis?
No. BMI is a screening measure. For ages 12 through 19 it must be interpreted using age- and sex-specific growth references, and a clinician considers growth history and other health information.
Is BMI different for men and women?
For adults, no. The formula and the category thresholds are identical for men and women. Sex matters for ages 12 through 19, where BMI is read against a growth reference specific to sex and to age in months, which is why the calculator asks.
What is a healthy BMI range?
For adults, a BMI from 18.5 to below 25 is described as a healthy weight. The calculator converts that band into the weight range it corresponds to at the height entered, and shows how far the entered weight sits from the nearest edge of it.
What does the BMI scale mean?
The adult BMI scale runs from underweight below 18.5, through a healthy weight from 18.5 to below 25, overweight from 25 to below 30, and three classes of obesity from 30 upward. The BMI chart on this page lists every band. The scale describes where a figure sits among adults generally; it does not describe an individual body.
How do I calculate BMI in kg?
Choose metric units and enter height in centimetres and weight in kilograms. The metric BMI equation is weight in kilograms divided by height in metres squared, so 70 kg at 1.75 m gives 70 divided by 3.0625, which is a BMI of 22.9. The calculator converts the centimetres you type into metres before squaring them.
Does BMI work the same way for teenagers?
No. Between 12 and 19 the same BMI means different things at different ages, so it is compared against CDC BMI-for-age references for that sex and month of age and reported as a percentile rather than placed in an adult band.
Can BMI be used during pregnancy?
BMI is not a suitable screening measure during pregnancy, because the weight change of pregnancy is not what the adult bands describe. Pregnancy weight is followed with guidance from a midwife or doctor instead.