How to calculate BMI by hand with the BMI formula

How to calculate BMI by hand with the BMI formula

There are dozens of BMI calculators online. In fact, we have a BMI calculator you can use if you’re in a hurry to know your body mass index. But did you know that you don’t need an online calculator to calculate your body mass index at all? You can do it by hand, with just a pencil and a piece of paper.

In this article, you’ll learn:

  • How to convert imperial measurements to metric
  • The formula for calculating BMI
  • How to interpret your body mass index

Ready? Read on and take notes; you’re going to learn how to calculate BMI by hand!

The BMI Formula

The BMI formula is simple to remember. When it’s written out, the formula for calculating your BMI looks like this:

weight (kg) / [height (m)]2

 All that means is this: you’ll take your weight in kilograms and divide it by your height in meters. Then take that answer and divide it by your height in meters again. That’s it! That’s all there is to it.

You can actually switch that formula around a little bit, too. If it’s easier for you, multiply your height in meters by itself. Then, divide that into your weight in kilograms. The answer will be the same, but the math might be a little easier for you. Particularly if you hate division!

Taking Your Measurements

Obviously, one of the first things you’ll need to do to find your BMI is to take your measurements. You’ll need both your height and your weight. You can measure yourself in inches and pounds or in meters and kilograms. However, remember that the formula for BMI is in metric measurements.

If you choose to take your measurements in inches and pounds, you’ll find that there’s an additional step: converting your measurements to metric. The easiest way to convert inches to meters is to multiply the inches by 2.54. Then, divide that by 100. That’s it! So a person who is 67 inches tall would multiply 67 by 2.54 and get 170.18. Divide by 100, and you’ll get 1.7 meters.

If you choose to take your weight in pounds, you’ll convert this to kilograms. To do this, you’ll need to know that one pound is equal to .453592. That means that you’ll take your weight in pounds and multiply that number by .453592. If you don’t want to be that exacting, you can use .45, and you’ll get a number that’s “close enough.”

If you’ve chosen to take your measurements in kilograms and meters, then you’re all set! There’s nothing more you need to do before you calculate your BMI. Just jot down your measurements and you’re good to go.

Make sure you measure yourself accurately, so that you can be sure your BMI is calculated correctly.. When you take your height, it’s best to have a friend help. Stand tall with your heels and your shoulders touching the wall. Then, have him mark a point on the wall that’s even with the topmost part of your head. If you have “big” hair, that doesn’t count!

With Your Pen, Calculate BMI by Hand

We won’t lie: there’s a lot of math involved with calculating BMI by hand. Fortunately for you, there are calculators if you’re uncertain of your math skills. Don’t be afraid to pull out the calculator on your phone, or to grab the calculator from your coworker’s desk.

To make things easier for you, begin with your measurements in metric. This will reduce the number of steps you need to take to calculate your BMI. Just divide your weight by your height twice, and you’re done.

Again, if you like, you don’t have to divide twice. Just multiply your height in meters by itself. Then divide that answer into your weight in kilograms. The resulting answer is still your Body mass index, but some people find that this method is easier than calculating out so much division.

Fill in the Numbers in the Formula and Calculate

All that’s left for you to do is fill the numbers into the BMI formula and calculate! Of course, you may be wondering what to do with your BMI once you’ve calculated it.

Your BMI is an indication of your health. If you’re aged 220 or older, your body mass index can help determine whether you’re at risk for certain diseases. People who are overweight or obese are at a higher risk of some cancers, like breast cancer and prostate cancer. They’re at a higher risk for heart disease, heart attack and stroke. They’re also more likely to be diagnosed with Type 2 diabetes, high blood pressure and high cholesterol.

If your body mass index is 30 or higher, it’s time to talk to a doctor. You can begin to make lifestyle changes immediately by eating healthier foods, exercising more and living a less sedentary life.

If your body mass index is 40 or higher, you are considered morbidly obese. Please consult your doctor before you begin exercising. Together you and your healthcare practitioner can determine whether exercise is safe for you. You may also be eligible for bariatric surgery.

Does your body mass index fall below 18.5? You’re considered under the healthy range, which means you’re at risk for a unique set of health problems. Anemia, malnutrition and fertility problems are among these issues.

That said, if you’ve calculated your BMI by hand and your body mass index falls between 18.5 and 24.9, congratulations! You’re considered to be in a healthy weight range, so keep up the good work!


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