Our BMI calculator gives the BMI number for the corresponding weight and height put into the calculator.

Here you will have the option to type in your height and weight in feet and pounds or metric units to see your body mass index.

This calculation is for adult BMI, so 18 years and older. It is not always perfectly accurate for children and adolescents.

What is BMI?

BMI, or Body Mass Index, is a person’s weight in kg (or pounds) divided by the square of height in meters (or feet and inches).

In a more clearly written form, the formula is BMI = weight (kg) / [height (m)]2 for the more common metric formula, or BMI = weight (lb) / [height (in)]2 x 703.

The simple calculation is used for the inexpensive screening of clients and patients.

The purpose of BMI screening is not to measure body fat but to look for correlations with the direct measures of body fat.

It is still considered to be a body composition formula.

BMI correlates with many health problems, such as metabolic and disease outcomes like heart disease and other health risks.

BMI Chart Ranges

When you receive your BMI number, you will be put into one of four weight status levels based on BMI ranges.

BMIWeight Status
< 18.5Underweight
18.5 – 24.9Normal weight/Healthy weight
25.0 – 29.9Overweight
30.0 and higherObesity

These can also be paired with weight ranges and growth charts for healthcare providers to see high BMI and ideal weight.

These factors can be used when finding life insurance rates and medical advice.

The CDC, or the Centers for Disease Control and Prevention, along with the World Health Organization, stand by the use of body mass index for finding health information and increased risk factors.

To look at the BMI of children and adolescents, BMI is shown as a percentile ranking.

Current BMI Trends

The rise in obesity and decrease in overall physical activity in the US has caused the level of obese status for BMI to rise.

Average body weight has risen significantly in today’s world, and this is due to the modern world not involving much exercise and the change in jobs to involve more time sitting at a computer.

Along with the rise in BMI levels, we have increased prevalences of chronic diseases, type 2 diabetes, and high blood pressure.

It is important to know about the rise in average BMI so that we can work to counteract it in the fitness industry.

BMI Accuracy

BMI is an easy and inexpensive option for screening, and it should primarily be used for that alone and not focused on too intensely.

It is extremely accurate for the general population, but it is not without limitations.

BMI is not extremely accurate for either extreme of the spectrum where someone has excessive amounts of muscle mass or is extremely lean.

This typically means for athletes and those who train often. The BMI will be distorted one way or the other.

When someone has excessive muscle mass or has undergone significant weight loss, this could show them as unhealthy in either the low weight status or overweight and obese for populations like bodybuilders.

This happens because BMI is simple and doesn’t use any measurements to show how the body is composed.

If we wanted to make BMI a little more accurate, we would use a model with waist size factored into the calculation.

This would allow the measure to consider where the weight is held in the body. We typically see more weight held in the waist area when someone is unhealthy.

Some other factors to consider regarding the accuracy of BMI are the differences in averages for both sexes and their retention of fat, along with the difference in race and age.

This backs up the fact that BMI is excellent for screening, but on its own; it has some problems regarding overall health judgments.

The accuracy of BMI is higher when the BMI is high, and when there is a healthy BMI, it varies somewhat on other factors.

Health Consequences of Obesity

The following risks are higher in people with obese BMI levels:

  • Mortality risk
  • High blood pressure
  • Mental illnesses like depression and more
  • Gallbladder disease
  • Presence of cancers
  • Sleep apneas and other problems with breathing
  • Stroke
  • Coronary artery disease
  • High LDL cholesterol, Low HDL cholesterol, and high triglyceride levels
  • Chronic inflammation
  • Osteoarthritis

Other Methods for Testing Body Fat

Since BMI may not be the best indicator for Body Composition, there must be better ones out there, right?

There are many popular options for finding body composition in gyms and clinical settings.

Two of the popular ways that are currently done in gyms would be skinfold measurements and bioelectrical impedance.

Skinfold measures are done with a caliper to find the thickness of fat deposits under the skin in specific areas depending on your sex, race, and physical activity status.

The typical formula used is a 3 site skinfold measurement known as the Jackson and Pollock Protocol.

All you need for these measures to be done is a skinfold caliper, the proper formulas, and some expertise in doing the process.

And the other popular way to measure body composition is through the use of bioelectrical impedance, or BIA.

This BIA method estimates body composition through an electric current flowing through the body.

The idea behind its function is that electricity travels through muscle mass and body fat differently, so we can see the impedance the body has for the electricity measured with the scale/device.

Both of these two methods discussed are popular and rather easy and inexpensive to do, but the skinfold measure does require some level of expertise and practice with the use of the caliper.

Other popular methods are usually done on high-level athletes and in clinical settings.

These methods include underwater weighing, dual-energy x-ray absorptiometry, isotope dilution, and BOD POD.

These aforementioned methods are all rather expensive and require a lot of equipment to complete, but, of course, they are much more accurate.

Tyler Read - Certified Personal Trainer with PTPioneer

Tyler Read


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