NASM'S BMI CALCULATOR

BMI Calculator

BMI, or Body Mass Index, is more than just a number; it's a key indicator of weight-related health used by everyone from fitness experts to doctors. By simply looking at your height and weight, BMI gives an overview of your health status. However, it's important to note that while BMI is an effective tool, it doesn't always differentiate between muscle and fat. But it's still a prime predictor of potential health concerns.

Here, we'll guide you through understanding, calculating, and interpreting BMI for both you and your clients. BMI is used by personal trainers, nutrition, coaches, physicians, and epidemiologists to categorize body weight based on person's height and weight.

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What is BMI?

BMI, or Body Mass Index, is a key metric doctors rely on to gauge the relationship between your weight and overall health. Depending on where you are in the world, you might calculate BMI using metric or imperial units, with the metric system being more widely adopted.

After determining your BMI, it's categorized to provide insights into your weight status. It's important to remember that age factors in too. Those over 20 are in the adult category, while kids between 2 and 20 fall under a different bracket. For the tiny tots under 2, there's a distinct scale altogether.

How to calculate bmi

Understanding your Body Mass Index (BMI) is simple when you have your weight and height at hand. Here's how you can work it out:

In metric measurements:

BMI = weight in kilograms ÷ (height in meters squared)

For imperial measurements:

BMI = 703 × weight in pounds ÷ (height in inches squared)

Let's use Mary as an example:

Mary weighs 160 lb (approximately 72.57 kg) and is 5 ft 7 in. (which is 67 inches or 1.70 meters). Plugging these values into either formula, we find that Mary's BMI is 25.1.

bmi chart

For adults, BMI is grouped into specific categories that reflect a range of weight statuses, from "very severely underweight" to "very severely obese". These classifications are rooted in typical data from the general population. The chart provided (Table 1) is tailored to the American population, but it's worth noting that variations exist based on regional standards in different countries.

Is BMI calculated differently for males and females?

The Body Mass Index (BMI) is a universal tool used to categorize weight in adults, irrespective of gender. Interestingly, given the inherent physiological differences between men and women, women generally possess a slightly elevated body fat percentage at an identical BMI. This distinction is where body fat scales can offer enhanced insights into the unique body compositions of both genders. Refer to the table for a breakdown of body fat percentages delineated by biological sex. Now, BMI works pretty well if your height is around the average. But if you're notably shorter or taller than most, it might not be as accurate. In simpler terms, shorter folks might find BMI paints them as having more body fat than they do, while taller individuals might find the opposite.