How to Calculate BMI: BMI Formula, Categories & Examples

Q: What is BMI?

BMI, or Body Mass Index, is a screening measure that compares a person's weight with their height.

Q: What is the BMI formula?

The BMI formula is weight in kilograms divided by height in meters squared: BMI = weight (kg) / height (m)².

Q: What is a healthy BMI range for adults?

For adults, a BMI from 18.5 to 24.9 is commonly classified as the healthy or normal range.

BMI, or Body Mass Index, is a commonly used screening measure that compares a person's weight with their height. Learning how to calculate BMI can help you understand your BMI number and the standard BMI categories used for adults.

Calculate Your BMI Quickly

Instead of calculating the formula manually, use our free online BMI Calculator to get your BMI result quickly.

Use the BMI Calculator

What Is BMI?

BMI stands for Body Mass Index. It is a numerical value calculated from a person's weight and height. BMI is commonly used as a screening tool to place adults into general weight categories.

BMI does not directly measure body fat. It is a simple calculation that can provide a general starting point when looking at body weight in relation to height.

How to Calculate BMI

To calculate BMI using metric measurements, divide your weight in kilograms by your height in meters squared.

BMI = Weight (kg) ÷ Height (m)²

For example, suppose a person weighs 70 kilograms and is 1.75 meters tall.

Example BMI Calculation

Weight = 70 kg

Height = 1.75 m

BMI = 70 ÷ (1.75 × 1.75)

BMI = 70 ÷ 3.0625

BMI ≈ 22.86

This value falls within the commonly used healthy BMI category for adults.

How to Calculate BMI Using Pounds and Inches

BMI can also be calculated using weight in pounds and height in inches.

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

The number 703 is used to convert the imperial measurement system into the equivalent BMI value used with the metric formula.

If you already know your weight in kilograms and height in meters, the metric formula is simpler.

BMI Categories for Adults

For adults, BMI values are commonly grouped into the following categories:

BMI Range	Category
Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 or higher	Obesity

These categories are general screening ranges for adults. A BMI result should not be considered a diagnosis or a complete assessment of an individual's health.

Why Calculate BMI?

A BMI calculation can provide a quick way to compare weight with height. It is commonly used in health research, population studies and general health screening.

People may calculate BMI to:

Understand their approximate BMI category
Track changes in body weight over time
Discuss weight-related information with a healthcare professional
Use BMI as one part of a broader health assessment

What Is Considered a Healthy BMI?

For adults, a BMI between 18.5 and 24.9 is commonly classified as the healthy or normal range.

However, BMI should be interpreted carefully. Two people with the same BMI may have different amounts of muscle, fat and other body composition characteristics.

BMI Example: A Different Calculation

Consider a person who weighs 90 kilograms and has a height of 1.80 meters.

Step-by-Step Example

Weight = 90 kg

Height = 1.80 m

BMI = 90 ÷ (1.80 × 1.80)

BMI = 90 ÷ 3.24

BMI ≈ 27.78

Based on the standard adult categories, this BMI falls within the overweight range.

BMI vs. Body Fat

BMI is not the same as body fat percentage. BMI uses only weight and height, while body fat percentage attempts to estimate how much of the body is made up of fat.

A person with a high amount of muscle may have a higher BMI because muscle contributes to body weight. Therefore, BMI should be viewed as a screening measurement rather than a complete measurement of body composition.

Who Should Be Careful When Using BMI?

Standard adult BMI categories may not be appropriate for everyone. For example, athletes with significant muscle mass may have a higher BMI without having excessive body fat.

BMI is also interpreted differently for children and teenagers, where age and sex are important factors. Pregnancy also requires different considerations.

If you have concerns about your weight, health or nutritional needs, consider discussing your results with a qualified healthcare professional.

How to Use Our BMI Calculator

Our free BMI Calculator makes the calculation simple. You only need to enter your height and weight.

Open the BMI Calculator.
Enter your height.
Enter your weight.
Click the calculate button.
Review your BMI result and category.

Try the Free BMI Calculator

Calculate your BMI in seconds without doing the formula manually.

Calculate BMI

BMI and Other Health Calculators

BMI is only one type of health-related calculation. You may also find our other free health and fitness calculators useful.

Try our BMR Calculator to estimate your Basal Metabolic Rate, or use our Calorie Calculator to estimate daily calorie needs.

You can also explore our Ideal Weight Calculator and Water Intake Calculator.

Related Health & Fitness Tools

Explore all of our free Health & Fitness Calculators for additional tools and estimates.

BMI Calculator FAQs

What is BMI?

BMI stands for Body Mass Index. It is a screening measure that compares a person's weight with their height.

What is the BMI formula?

The metric BMI formula is: BMI = weight in kilograms ÷ height in meters squared.

What is a healthy BMI range for adults?

A BMI from 18.5 to 24.9 is commonly classified as the healthy or normal range for adults.

Is BMI a complete measure of health?

No. BMI is a screening measure and does not directly measure body fat or account for factors such as muscle mass, age, sex or overall body composition.

Can I calculate BMI without a calculator?

Yes. You can use the BMI formula manually by dividing your weight in kilograms by your height in meters squared. However, an online BMI Calculator makes the process faster and reduces calculation errors.

Can children use the adult BMI categories?

Adult BMI categories should not be applied directly to children and teenagers. BMI for children and teenagers is generally interpreted using age- and sex-specific growth charts.

Important BMI Disclaimer

The information on this page is provided for general educational and informational purposes. BMI is a screening measurement and should not be used as a diagnosis or as a substitute for professional medical advice.

If you have concerns about your weight, diet, exercise or overall health, consult a qualified healthcare professional.

Explore More Free Calculators

Easy Online Tool provides free calculators for math, finance, health, fitness, dates, conversions and everyday calculations.

View All Tools