BMI CALCULATOR

Your BMI is a measurement of your body fat based on your height and weight. Although your BMI does not actually “measure” your percentage of body fat, it is a useful tool to estimate a healthy body weight based on your height. Due to its ease of measurement and calculation, it is the most widely used diagnostic indicator to identify a person’s optimal weight depending on his height. Your BMI “number” will inform you if you are underweight, of normal weight, overweight, or obese.

BMI is an estimate of body fat and a good gauge of your risk for diseases that can occur with more body fat. The higher your BMI, the higher your risk for certain diseases such as heart disease, high blood pressure, type 2 diabetes, gallstones, breathing problems, and certain cancers. However, due to the wide variety of body types, the distribution of muscle and bone mass, etc., it is not appropriate to use this as the only or final indication for diagnosis.

Body Mass Index Formula

The formulas to calculate BMI based on two of the most commonly used unit systems:

BMI = weight(kg)/height²(m²) (Metric Units)
BMI = 703·weight(lb)/height²(in²) (U.S. Units)

• • • Ponderal Index

      Similar to BMI, the Ponderal Index (PI) is a measure of leanness of a person. It was also called Rohrer’s index. Comparatively, the Ponderal Index is more even for different stature. Therefore, it was commonly used in pediatrics.

      PI = weigh

BMI Table for Adults

This is the World Health Organization’s (WHO) recommended body weight based on BMI values for adults. It is used for both men and women, age 18 or older.

According to the BMI scale, if you fall between 18.5 and 24.9 you’re considered to be a normal, healthy weight. If you clock in below 18.5, you are considered underweight. On the other side of the scale, if you’re between 25–29.9 this that you’re overweight. And, finally, if your BMI is higher that any higher than 30 means that you are obese. (If you’re curious about how the number is determined, BMI is calculated by dividing weight in kilograms by height in meters squared.)

Body Mass Index Advantages and Disadvantages

Advantages: Accurate Measurements Across a Group

Body mass index works well for what it was intended to do; measure rates of obesity in a population. Because it’s a general measure of obesity that will work for most people, looking at changes in BMI level allow researchers to get a good idea of how rates of overweight and obesity differ over time, or between populations, explains the Centers for Disease Control and Prevention. Because it’s a relatively simple way to measure obesity in a population, this allows health researchers to more easily gather data they can use to investigate the obesity epidemic or, for example, look at how dietary patterns affect the risk of obesity in large groups of people. It’s not prohibitively expensive to measure — unlike, for example, body fat measurements — so researchers can afford to can look at larger groups of study subjects to pick out trends in larger segments of the population

BMI can also help your physician gauge your general risk of obesity-related diseases, though BMI is best used in combination with other measurements to get a more complete look at your health.

Disadvantage: BMI Misses Normal Weight Obesity

Because BMI is simply a measure of your weight versus your height, it doesn’t take into account where that weight comes from — lean tissue or fat. For this reason, you might have a normal “healthy” weight, according to your BMI, but still face health risks due to excess body fat. For example, excess abdominal fat that pushes your waistline to larger than 35 inches for women and 40 inches for men ups your risk of obesity-related diseases, according to the National Institutes of Health, regardless of your BMI. And normal weight obesity — which happens when you’re overfat, but not overweight, according to BMI — increases your blood lipid and blood pressure levels, which increases your risk of heart disease.

Disadvantages: BMI Overestimates Risk for Some

While BMI might underestimate the risk for people with normal weight but high body fat, it can overestimate the risk for muscular, healthy people. Someone putting in serious time at the weight room might have a body weight that pushes their BMI into the “overweight” or “obese” category, even if they carry very little body fat — and therefore have a lower risk of obesity-related diseases than someone at the same weight with more fat tissue.

BMI also doesn’t distinguish between the type of fat you carry — subcutaneous or visceral fat. While subcutaneous fat — the fat you see under your skin, which you can pinch — affects the way you look, it’s visceral fat — “hidden” fat located deep in your abdomen that surrounds your internal organs — that poses the highest health risk. If you’re slightly overweight, but most of your fat is from subcutaneous fat — for example, in your hips and thighs — you’ll face a lower health risk than someone who has the same weight and fat level, but stores most of his fat as harmful visceral fat.

Take a Holistic Approach to Measurements

Take a more holistic approach and use several measurements to asses your weight and health. In addition to BMI, consider your waist size — to ensure you’re under the recommended waist size for your gender. Instead of measuring weight reduction in terms of where you fall on the BMI scale, look at a combination of pounds and inches lost and consider a professional body fat measurement to get an accurate look at whether you have a healthy body fat level.

Stay motivated and happy with your health routine by focusing on performance-based goals instead of simply aiming to fall into a certain BMI range. Reward yourself for making healthful meals at home for the week, eating your recommended intake of veggies for the day, running faster without losing your breath, or lifting a heavier weight during your workouts, for example, rather than being able to check the “normal weight” box when it comes to BMI.