Free Online BMI Calculator

Calculate your Body Mass Index (BMI), BMI Prime, and Ponderal Index. This free, browser-based tool helps you assess whether your weight is in a healthy range based on your height. No signup required.

How to Use the BMI Calculator

Calculating your Body Mass Index (BMI) is quick and easy. Follow these simple steps:

• 1
  Choose Your Units: Select your preferred measurement system (Metric or US Units) from the dropdown menu.
• 2
  Enter Age & Gender: Input your age and select your gender. This helps determine the correct percentile category if the subject is under 20 years old.
• 3
  Input Height: Enter your height in centimeters, or in feet and inches (depending on your selected unit system).
• 4
  Input Weight: Enter your weight in kilograms or pounds.
• 5
  Calculate: Click the "Calculate BMI" button. Your BMI, BMI Prime, and Ponderal Index will be displayed instantly, along with a visual gauge showing where you fall on the scale.

What is BMI?

Body Mass Index (BMI) is a numerical value of your weight in relation to your height. It is a simple, inexpensive, and noninvasive screening method used to identify possible weight problems for adults. However, BMI is not a diagnostic tool. For example, a person may have a high BMI, but to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments.

BMI Formula

BMI Prime

BMI Prime is a ratio of a person's actual BMI to their upper limit "healthy" BMI (usually defined as 25).

A BMI Prime less than 0.74 indicates underweight, between 0.74 and 1.0 is optimal, and greater than 1.0 indicates overweight.

Ponderal Index

The Ponderal Index (PI) is similar to BMI but uses the cube of the height instead of the square. It is often used for more extreme heights or heights where BMI might be inaccurate.

BMI Table for Adults

BMI Table for Children and Teens (Age 2-20)

BMI is interpreted differently for children and teens. It is age- and sex-specific and is referred to as BMI-for-age. A child's weight status is determined using an age- and sex-specific percentile.

BMI Charts for Children and Teens (Reference)

Below are simplified reference points for BMI percentiles based on CDC growth charts. Use these to locate the calculated BMI on the chart corresponding to the child's age and gender.

Health Risks

Limitations of BMI

While BMI is a useful screening tool, it has limitations:

• Overestimates body fat: In athletes and individuals with high muscle mass. For a more accurate measurement, we recommend using our body fat calculator or navy body fat calculator.
• Underestimates body fat: In the elderly or individuals who have lost muscle mass.
• Does not measure fat distribution: It does not distinguish between visceral fat (belly fat) and subcutaneous fat.
• Ethnicity variations: Some ethnic groups may have different health risks at the same BMI (e.g., Asians may have higher risks at lower BMIs).

Frequently Asked Questions (FAQ)

What is BMI Prime?

BMI Prime is the ratio of your actual BMI to the upper limit of the "healthy" BMI range (which is 25). A BMI Prime between 0.74 and 1.0 means you are in a healthy weight range. It is simply another way to look at your BMI score.

What is the Ponderal Index?

The Ponderal Index (PI) is similar to BMI, but it cubes your height instead of squaring it. PI is considered a more accurate measure of body mass for individuals who are very tall or very short, where standard BMI might be misleading.

Is BMI accurate for athletes or bodybuilders?

BMI has limitations. Because it only calculates weight relative to height, it does not distinguish between muscle mass and fat mass. Highly muscular individuals may register as "overweight" or "obese" on the BMI scale despite having very low body fat. For precise body composition, a body fat calculator is recommended. To understand why, read our complete guide on BMI vs. Body Fat Percentage.

Why is BMI different for children and teens?

For children and teens (ages 2-20), BMI is calculated the same way but interpreted differently. Because body fat changes with age and differs between boys and girls, their BMI is compared to growth charts and expressed as a percentile rather than a standalone category.

Does this calculator store my health data?

No. Your privacy is our priority. All calculations happen directly in your web browser. We do not collect, save, or transmit your height, weight, or any other personal information to our servers.

What is a healthy BMI range?

For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight. A BMI below 18.5 is classified as underweight, 25 to 29.9 is overweight, and 30 or above is considered obese. If your goal is weight loss, you might find our calorie deficit calculator or keto macro calculator helpful. You can also read our guide on how many calories you should eat to lose weight.