BMI Calculator

BMI Calculator

The BMI Calculator is a tool that measures your body mass index, also known as the BMI. This should not be confused with the Body Fat Calculator.

Your body fat percentage is totally different from your body mass index. While the body fat percentage is measured using your body measurements, BMI is measured based solely on your height and weight.

You don’t have to be a fitness expert to be concerned about your BMI. It’s a pretty good, general measuring stick, to your overall physical condition. But it has its flaws, and with certain body types, it is not an accurate indication of your fitness level.

BMI Calculator

* In the table below, select Imperial in the USA, and Metric for most other countries.

BMI Guidelines

Here are the BMI ranges from the CDC for determining body mass based on the calulation above: (1)

  • Underweight = <18.5

  • Normal or Healthy Weight = 18.5–24.9

  • Overweight = 25–29.9

  • Obesity = BMI of 30 or greater

Your BMI is only a general guideline in measuring your physical fitness. It is not an accurate measure of body fat percentage, and does not account for muscle mass, body composition, or bone density.

It will be misleading if you have a muscular frame, large-boned frame, or a dense body composition. A better measurement is the body fat calculator.

Knowing your BMI is important if you want to generally know your fitness level. In many cases, it’s a pretty good predictor of your fitness level, as well as whether or not you are overweight, or a healthy weight.

Is BMI Accurate?

BMI is not perfect and has its flaws. It simply does not work for some body types, and is not an accurate measure of certain people’s physical fitness. See more below. It is better used as a general guide based on the average person’s body type and physical build.

What is the BMI (Body Mass Index)?

Also known as the body mass index, calculation of the BMI is best for adults 20 years old and above. Children above 2 years old use BMI percentile simply because they are still at the growing stage; their height would increase rapidly through the years and their weight can go through a lot of changes too.

How to Measure BMI

Here are the formulas used to measure BMI:

1. Metric BMI Formula:
Weight (kg) / Height (m)²

2. Imperial BMI Formula
(Weight (lbs.) * 703) / Height (inches)²

What Does BMI Measure?

Unlike measuring body fat percentage, BMI doesn’t measure actual body fat. It only measures your body fat based on the relation of your weight and height.

While you can certainly visit your doctor or fitness professional to get help measuring your BMI, you can easily use automatic tools such as the BMI calculator above.

Knowing your BMI helps you come up with potential weight issues. However, you must also know that there are other ways to measure body fat that are considered more accurate than BMI. This includes using the body fat percentage calculator, skinfold thickness measurements, underwater weighing, dual-energy X-ray absorption, and bioelectrical impedance. (2)

However, measuring your BMI is just as useful if you simply want to be aware of where your weight stands according to your height, and if there’s anything you should be worried about at all.

Simply put, by knowing your BMI with a BMI calculator, you may know whether you’re on a normal weight level, underweight, overweight or obese based on your height.

Your Ideal Body Mass Index

BMI CalculatorThe ranges for BMI for both men and women share the same figures. Since BMI is calculated using measurements of your height and weight, a person can share the same weight with someone and stay on the healthy level, while the other may be considered overweight.

Example of Misleading BMI

For example, an adult man who stands 5 feet 8 inches and weighs 160 pounds has a BMI of 24.3. He falls under the normal weight category. Another adult male with the same height but weighs 170 pounds because he is muscular and fit would have a BMI of 25.8, which is considered overweight. So BMI must be adjusted accordingly based on your muscle mass!

However, being categorized as underweight or overweight based on your BMI alone doesn’t automatically mean you have a weight issue to worry about. While it’s best to aim for a normal or healthy weight-level category, you can be underweight or overweight yet remain healthy at the same time.

The Flaw in using the BMI Calculator

Some people are actually very healthy but aren’t in the normal range for BMI because of their physique and bone structure. For instance, athletes who have a high muscle percentage, or even someone who is generally dense and large-boned, can have a very high BMI and actually be in very good shape. So it is not a perfect indicator of fitness level, and should be used as a general guide.

It will provide a very misleading and unrepresentative value if you are:

  • Have a muscular body
  • Are a large-boned person
  • Have a dense body composition

After you calculate your BMI, see if you are in the normal range. If you are, that is terrific…keep up the great work! If you’re are out of range, check with your healthcare provider on your overall fitness level. You might find that you have a high fitness level, but a misleading BMI.

Click to return to the homepage, or you can also click to see more tools in the toolbox.

Picture of David Williams

David Williams

A diet and fitness enthusiast, David is an ex-Army Airborne Ranger and Infantry soldier with decades of fitness and wellness experience. A West Point graduate with a degree in engineering, he focuses on technical research related to fitness, nutrition, and wellness. He loves the beach and working out, and spending time with his wife and daughters.

See All Posts


  1. Centers for Disease Control and Prevention. (2022, June 3). About adult BMI. Centers for Disease Control and Prevention.
  2. Frey, M. (2022, July 26). Bioelectrical impedance analysis (BIA)? Verywell Fit.

Click to see our medical disclosure.