What is a BMI calculator?

Your body mass index (BMI) estimates whether your weight is healthy for your height. Although BMI isn’t perfect, it lets you know if you’re exposed to potential health risks from being under or overweight.

A BMI calculator lets you measure your BMI from your height and weight measurements. With our calculator, you can enter imperial (feet and pounds) or metric (cm and kilograms) units.

Body mass index is a simple way to assess whether your weight falls within a healthy range for your height. But it doesn't consider factors like muscle mass or distribution of fat.

A BMI calculator gives you a general idea if you’re a healthy weight for your height.

How to calculate BMI

Calculating BMI is pretty simple. Your BMI is your weight divided by your height squared.

Using imperial units:

BMI = weight (lb)×703 / height (in)2

Using metric units:

BMI = weight (kg) / height (m)2

What does your BMI result mean?

Men and women over 20 years old categorize BMI results into four standard ranges:

• Underweight - BMI less than 18.5
• Healthy weight - BMI 18.5–24.9
• Overweight - BMI 25–29.9
• Obesity - BMI 30 and above

Say you’re calculating BMI in metric units. You weigh 85 kilos and are 1.85 meters tall.

BMI = 85 divided by 3.42 (height squared) = 24.8

So your BMI result means you’re in the healthy weight range.

You categorize BMI differently for kids and teens (under 20 years old). The BMI result is ranked as a percentile, comparing it to kids of the same age and sex.

BMI for kids and teens has four percentile categorizations:

• Underweight - Less than 5th percentile
• Healthy weight - 5th percentile to less than 85th percentile
• Overweight - 85th percentile to less than 95th percentile
• Obesity - Equal to or greater than the 95th percentile

What are the limitations of BMI?

Measuring BMI has five main limitations.

1. Doesn't distinguish between muscle and fat

BMI doesn't differentiate between muscle mass and body fat. As a result, muscular people, such as athletes, may be categorized as overweight or obese despite having low body fat.

2. Ignores fat distribution

BMI doesn't account for where fat is distributed in the body. Abdominal fat carries a higher health risk, but BMI doesn't distinguish it from fat in other areas.

3. Doesn't consider age, gender, or ethnicity

BMI doesn't adjust for age, gender, or ethnicity. For example, older adults naturally have more body fat than younger people, women tend to have more body fat than men, and certain ethnic groups may have different health risks at the same BMI.

4. Not accurate for all populations

It may not be reliable for children, teenagers, older adults, pregnant women, or those with certain health conditions. For example, older adults might have a normal BMI but still have a high body fat percentage.

5. Doesn't measure overall health

BMI is a basic screening tool. It doesn't consider other factors like diet, activity level, blood pressure, cholesterol, or overall fitness, which are critical for assessing health.