BMI Calculator (Body Mass Index Calculator)

What Is BMI?

Body Mass Index, commonly called BMI, is a simple measurement that compares a person’s weight with their height. It is widely used as a screening measure to help categorize weight relative to height in adults.

BMI does not directly measure body fat. Instead, it provides a numerical value that can be considered alongside other information when looking at general weight-related health patterns.

Because the calculation requires only height and weight, it is quick and easy to use.

How to Calculate BMI

The formula depends on whether you use metric or U.S. customary measurements.

For metric measurements:

BMI = Weight (kg) ÷ Height² (m²)

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

BMI = 70 ÷ (1.75 × 1.75)

BMI = 70 ÷ 3.0625

BMI ≈ 22.9

For pounds and inches, the commonly used formula is:

BMI = [Weight (lb) ÷ Height² (in²)] × 703

The BMI Calculator performs these calculations automatically after you enter the required height and weight.

Understanding Adult BMI Ranges

For most adults, commonly used BMI categories are:

• 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 rather than a diagnosis. A person’s overall health cannot be determined from BMI alone.

Age, body composition, muscle mass, medical history, lifestyle, and other factors may provide additional context.

For more information about BMI and healthy weight, visit the Centers for Disease Control and Prevention.

Why Height and Weight Matter

Two people can have the same weight but very different BMI values if their heights are different. Likewise, two people of the same height can have different values because their weights differ.

This is why both measurements are necessary.

When entering your information, use accurate measurements whenever possible. Small errors in height can noticeably affect the result because height is squared in the formula.

Limitations of BMI

BMI is useful as a simple screening measurement, but it has important limitations.

It does not distinguish between muscle, fat, and bone mass. For example, a muscular athlete may have a relatively high BMI even when their body-fat level is not high.

BMI also does not show where body fat is distributed. Other measurements, such as waist circumference, may provide additional information in some situations.

Because of these limitations, a BMI result should be viewed as one piece of information rather than a complete assessment of an individual’s health.

BMI for Children and Teenagers

BMI interpretation for children and teenagers is different from adult interpretation.

For younger people, BMI is generally considered in relation to age and sex, often using growth charts and percentiles. Therefore, the standard adult ranges should not automatically be applied to children.

Parents or caregivers who have concerns about a child’s growth or weight should consider discussing them with an appropriate healthcare professional.

Our BMI Calculator provides a quick way to estimate your Body Mass Index using your height and weight.

Tips for a More Accurate Result

Measure your height without shoes and enter the measurement carefully. When checking weight, using a reliable scale under similar conditions can help provide more consistent results.

Also make sure you select the correct measurement units. Mixing kilograms with feet or pounds with meters will produce an incorrect calculation.

If your weight changes over time, you can calculate the value again to see how the numerical result changes.

You can use the BMI Calculator whenever you want to check how your BMI changes as your height or weight information is updated.

Using Your BMI Result

A BMI result can provide a quick reference point, but it should not be treated as medical advice or a diagnosis.

If you have questions about your weight, nutrition, physical activity, or health risks, a qualified healthcare professional can consider your individual circumstances and provide appropriate guidance.

For everyday informational use, BMI offers a simple way to understand the relationship between height and weight using a standardized mathematical formula.

Explore more useful health and everyday calculation tools on our Calculators page.