How To Use Your BMI Calculator Effectively

Woman with low body fat

What is BMI or Body Mass Index?

Body Mass Index (BMI) is a person’s weight in kilograms divided by the square of height in meters.
Conversely, it can be a person’s weight in pounds divided by the square of height in inches.
Body Mass Index can be arrived at in several ways, but they each have their pros and cons.

A full immersion in a pool of water is the most accurate way to know how much of your body is pure
fat, and how much is muscle. While it’s a very accurate test, it comes with a fair amount of expense and inconvenience.

Woman in water

Calipers are among some common tools used.

Calipers can be used to pinch the skin in various places, however, they are open to human error, and
aren’t as accurate as they should be.

Caliper used to measure body fat

BMI Calculator

Then there’s the Body Mass Index, or BMI Calculator. Your BMI is calculated using nothing more than your
height and weight as mentioned earlier.

BMI Calculator tape

How does BMI measure body fat?

There are a lot of numbers that can be used to determine your overall health status.

Your weight is one such number, but it doesn’t tell the entire story.

Another useful number is your body fat weight percentage; in other words, what percentage of your weight is composed of fat. Knowing that percentage will give you a better idea of how healthy your weight is, and how healthy you are overall.

How to calculate BMI

By using this formula, you can calculate your BMI. BMI = kg/m2 where kg is your weight in kilograms
and m2 is your height in meters squared for calculation in metric.

Or for calculation in pounds and inches use the following Formula: weight (lb) / [height (in)]2 x 703
Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by
a conversion factor of 703.

Example: Weight = 200 lbs, Height = 5’10″ (70″)
Calculation: [200 ÷ (70)2] x 703 = 28.69

Or you can make it easy on yourself and just get a BMI Calculator for Apple and Android device from:

Apple Store or Android Store This makes it an easy thing to calculate, but it also means that there can be flaws with those calculations for certain people.

A typical Smartphone

Who should not use a BMI Calculator?

For example, if you are a bodybuilder and have a high percentage of muscle mass, then your BMI may
be artificially inflated, and it won’t reflect the true nature of your overall health.

Photo by Damir Spanic on Unsplash

BMI should not be used by everyone

BMI is not used for muscle builders, long distance athletes, pregnant women, the elderly or young children. This is because BMI does not take into account whether the weight is carried as muscle or fat, just the number. Those with a higher muscle mass, such as athletes, may have a high BMI but not be at greater health risk. Those with a lower muscle mass, such as children who have not completed their growth or the elderly who may be losing some muscle mass, may have a lower BMI. During pregnancy and lactation, a woman’s body composition changes, so using BMI is not appropriate.” According to –Diabetes, Canada

Is it enough just to know your BMI?

Most people will find that the Body Mass Index will give them a rough idea of how healthy
their current weight is. however, this leads to the question of how somebody who is in great shape physically can weigh more than somebody who has a high body fat weight percentage.

The reason for this is that the same volume of muscle weighs more than the same volume of fat.

Muscle is denser than fat, and that’s why a muscular person, who appears thinner and more fit, can weight more than someone who looks flabby and unhealthy. To put it another way, how much you weigh isn’t the only way to judge if you’re obese or not.

Regular exercise makes a difference

If you are doing a lot of exercise while trying to lose weight, then you may wonder why the scale isn’t
reflecting how you feel. Understanding that fat and muscle each have a different density will explain it. Does that make sense?

Woman exercising

The scale only tells a part of the story

You may be working out a lot, and looking trim, but if you are adding a lot of muscle at the same time, then the scale may not indicate that fact.

The main thing is not to let this fact discourage you. As long as you are continuing to exercise and getting
healthy, you can pretty much ignore the scale.

Google Scale
Bathroom scale

Body Fat Weight Percentage

Knowing your Body Fat Weight Percentage is really the key to knowing how healthy your weight is.

Related: How to overcome emotional overeating

How to calculate Body Fat Weight Percentage

Step one

The first step is knowing the professional age-adjusted body fat percentage recommendations
based on


Age 20-40 yrs old: Under fat: under 21 percent,
Healthy: 21-33 percent, Overweight: 33-39 percent,
Obese: Over 39 percent

Age 41-60 yrs old: Under fat: under 23 percent,
Healthy: 23-35 percent, Overweight : 35-40 percent
Obese: over 40 percent

Age 61-79 yrs old: Underfat: under 24 percent,
Healthy: 24-36 percent, Overweight: 36-42 percent,
Obese: over 42 percent


Age 20-40 yrs old: Underfat: under 8 percent,
Healthy: 8-19 percent, Overweight: 19-25 percent,
Obese: over 25 percent

Age 41-60 yrs old: Underfat: under 11 percent,
Healthy: 11-22 percent, Overweight: 22-27 percent,
Obese: over 27 percent

Age 61-79 yrs old: Under fat: under 13 percent,
Healthy: 13-25 percent, Overweight: 25-30 percent,
Obese: over 30 percent

Step two

The second step is to weigh yourself at the same time each day for at least a month to arrive at
your average body weight.

Step three

The third step is to calculate your BMI by using either one of the apps you downloaded unto your device.

Step four

The fourth step is to use the gender-based formula that was published in the British Journal of Nutrition in 1991 to calculate your body fat percentage, as follows.


(1.20 x BMI) + (0.23 x Age)-5.4 = Body Fat Percentage


(1.20 x BMI) + (0.23 x Age)-16.2 = Body Fat Percentage

For example, if your BMI is 24.96, and you are a male age 74, your body fat percentage would be calculated by using the following formula:

(1.20 x 24.96) + (0.23 x 74) – 16.2 = 30.82 Body Fat percentage

Which would be considered Obese because it’s over 30 percent for someone in that age group.

Your Body Fat Weight Percentage is a better indicator

All of those other methods for determining your weight have their place, but it’s your body fat
weight percentage that will give you the best possible number for determining what your
“true weight” should be.

If your BMI or body fat weight percentage is higher than what you want it to be, then a slight change in your lifestyle or even your workout routine can make a big difference, as well as having the right equipment can enhance the effects and help you achieve the body you want.

2 thoughts on “How To Use Your BMI Calculator Effectively

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