Use this free BMI calculator with kg, cm, and age to calculate your Body Mass Index online. Enter your age, sex, weight, and height to get your BMI result and understand the appropriate BMI category.

For adults, BMI is calculated from weight and height using the standard BMI formula. For children and teenagers, BMI must be interpreted using age- and sex-specific BMI-for-age percentiles.

BMI Calculator kg with Age

Calculate BMI using kilograms and centimetres, with age-aware adult and child/teen interpretation.

Age

0 months 1 month 2 months 3 months 4 months 5 months 6 months 7 months 8 months 9 months 10 months 11 months

Use years and months for children and teens.

Sex

Male Female

Adult BMI formula and standard cutoffs are the same for men and women.

Units

Metric: kg + cm Imperial: lb + ft/in

Weight (kg)

Height (cm)

Weight (lb)

Feet

Inches

Example

5 ft 7 in

Pregnancy Standard adult BMI categories are not intended to assess weight status during pregnancy.

Calculate BMI Reset

BMI is a screening measure, not a diagnosis. Children and teens need age- and sex-specific BMI-for-age interpretation rather than adult BMI cutoffs.

What is BMI?

BMI (Body Mass Index) is a screening measure calculated from a person's weight and height.

For adults, BMI is calculated as:

BMI = weight (kg) ÷ height (m)²

For example, a person who weighs 70 kg and is 170 cm tall has a BMI of approximately 24.2 kg/m².

For adults aged 20 and older, standard BMI categories are underweight, healthy weight, overweight, and obesity. For children and teenagers aged 2 to 19, BMI is interpreted using age- and sex-specific BMI-for-age percentiles.

How to Use This BMI Calculator

Using this BMI calculator is simple:

1. Enter your age.
2. Select your sex.
3. Enter your weight in kilograms.
4. Enter your height in centimetres.
5. Click Calculate BMI.

You can also switch to pounds and feet/inches if you prefer imperial units.

For children and teenagers, entering the correct age is especially important because BMI is interpreted according to age and sex rather than adult BMI thresholds.

BMI Formula: How BMI Is Calculated

The standard BMI formula is:

BMI = Weight (kg) ÷ Height (m)²

If your height is given in centimetres, first convert it to metres:

Height in metres = Height in centimetres ÷ 100

For imperial units:

BMI = (Weight in pounds × 703) ÷ Height in inches²

Example

Weight = 70 kg
Height = 170 cm = 1.70 m

BMI:

70 ÷ (1.70 × 1.70) = 24.2 kg/m²

Adult BMI Calculator

For adults aged 20 and older, BMI is interpreted using standard adult BMI categories.

BMI	Weight Status
Below 18.5	Underweight
18.5 to less than 25	Healthy weight
25 to less than 30	Overweight
30 to less than 35	Obesity Class 1
35 to less than 40	Obesity Class 2
40 or greater	Obesity Class 3

The standard adult BMI categories do not change according to sex or age.

Women's BMI Calculator

A women's BMI calculator uses the same standard adult BMI formula as a men's BMI calculator.

For adults, BMI is calculated from weight and height:

BMI = weight (kg) ÷ height (m)²

The standard adult BMI categories are also the same for women and men.

This means that an adult woman and an adult man with exactly the same height and weight will have the same BMI value.

However, BMI does not measure body composition directly, so factors such as muscle mass, body-fat distribution, age, pregnancy, and overall health may need to be considered separately.

Male BMI Calculator

A male BMI calculator uses the standard adult BMI formula based on weight and height.

The calculation is:

BMI = weight (kg) ÷ height (m)²

The standard adult BMI categories are not different for men.

BMI is useful as a screening measurement, but it cannot distinguish muscle mass from body fat. This means that people with high muscle mass may have a higher BMI without the same body-fat level suggested by the BMI category alone.

Child BMI Calculator

Children and teenagers should not be classified using the standard adult BMI thresholds.

For ages 2 through 19, BMI is calculated from height and weight and then interpreted according to age- and sex-specific BMI-for-age percentiles.

The standard CDC screening categories are:

BMI-for-Age Percentile	Category
Below 5th percentile	Underweight
5th to below 85th percentile	Healthy weight
85th to below 95th percentile	Overweight
95th percentile or higher	Obesity

This is why the calculator asks for age and sex when calculating BMI for children and teenagers.

BMI Calculator by Age

Age affects how BMI should be interpreted.

For adults aged 20 and older, standard BMI categories are used regardless of age.

For children and teenagers aged 2 to 19, age is essential because BMI changes naturally during growth. The BMI value is therefore compared with other children of the same age and sex using BMI-for-age percentiles.

The important distinction is:

Adults: standard BMI categories
Children and teens: BMI-for-age percentiles

Healthy Weight Range Based on BMI

For adults, the standard healthy-weight BMI range is 18.5 to less than 25.

You can estimate the corresponding weight range for a given height using:

Lower weight = 18.5 × height²

Upper weight = 24.9 × height²

For example, at 170 cm:

Lower range ≈ 53.5 kg

Upper range ≈ 72.0 kg

This is a mathematical range based on standard BMI thresholds and is not a personalized medical target.

Can You Use BMI During Pregnancy?

Standard adult BMI categories are not intended to assess weight status during pregnancy.

Pregnancy changes body weight and body composition, so pregnancy-specific clinical guidance should be used instead of interpreting a normal adult BMI category as a pregnancy assessment.

How Accurate Is BMI?

BMI can be useful as a simple screening measure, but it has limitations.

BMI does not directly measure:

• body fat percentage
• muscle mass
• fat distribution
• bone mass
• individual health conditions

For example, someone with a high amount of muscle may have a high BMI without having the same body-fat level associated with that category.

For children, BMI should also be considered alongside growth patterns and other relevant health information.

Important

BMI is a screening measurement, not a diagnosis.

BMI Calculator Online: Quick Summary

BMI formula:
Weight (kg) ÷ Height (m)²

Adult healthy BMI range:
18.5 to less than 25

Adult BMI categories:
Underweight, healthy weight, overweight, and obesity

Women vs men:
The standard adult BMI formula and BMI categories are the same.

Children and teens:
BMI is interpreted using age- and sex-specific BMI-for-age percentiles.

BMI limitation:
BMI is a screening measure and is not a diagnosis.

BMI Calculator Online: Quick Summary

BMI formula:
Weight (kg) ÷ Height (m)²

Adult healthy BMI range:
18.5 to less than 25

Adult BMI categories:
Underweight, healthy weight, overweight, and obesity

Women vs men:
The standard adult BMI formula and BMI categories are the same.

Children and teens:
BMI is interpreted using age- and sex-specific BMI-for-age percentiles.

BMI limitation:
BMI is a screening measure and is not a diagnosis.

FAQ