BMI Calculator – How to Calculate BMI

Before choosing to undergo weight loss surgery, the first thing you need to know is your BMI. BMI stands for ‘Body Mass Index’, and the calculation is the ratio between your weight and your height. Enter your weight and height into our BMI Calculator to measure your own BMI.

What is BMI?

Your Body Mass Index indicates whether you are underweight, a healthy weight, overweight or obese in comparison to your height. It’s a vital tool for health professionals to determine your weight range before advising further action to take in regards to your weight loss surgery options.

The BMI is very useful for adults over 18 years of age. However, BMI can only act as an estimate for your weight as other factors such as your age, gender, bone density and body composition are not considered. It’s also important to note that BMI cannot determine your fitness level, which is another important factor for your overall health.

Calculating BMI

If you don’t have access to a BMI calculator, you can calculate BMI yourself with an easy BMI formula that involves dividing your weight (kilograms) by your height (metres). The answer then needs to be divided by your height again to get your BMI.

BMI Results and What They Mean

A healthy BMI range for most healthy adults is between 18.5 and 25. A BMI below 18 is underweight while a BMI over 30 is overweight or obese.

Less Than 18.5 – Underweight

Depending how underweight you are, you may need to put on some weight for the sake of your health. Your doctor or dietician will advise how to gain weight to ensure you are in a healthy weight range.

18.5 to 25 – Normal Weight

This is the ideal BMI to show that you’re in a healthy weight range. If you are within this weight range, you significantly reduce the chance of developing serious health problems.

25 to 30 – Overweight

You may be advised to lose weight to improve your health within this BMI range. Being overweight can negatively impact your overall health.

30 to 40+ – Obese

You’re at great risk of developing serious health problems if you are obese. A BMI over 30 shows that you are heavily overweight, and your doctor or dietician will strongly encourage you to take steps to lose weight.

Why BMI Matters

Being overweight can lead to a number of health conditions such as high cholesterol, high blood pressure, osteoarthritis, gallstones, decreased fertility and sleep apnoea.

Being overweight also significantly increases the chances of developing more serious health problems such as type 2 diabetes, heart disease, stroke and common cancers. By measuring your body fat, you can have a better idea of your current weight and ultimately get a good indication of your overall health.

BMI is Not Right for Everyone

Using a BMI calculator is not the best measurement of weight for everyone.

Athletes should not use the BMI method of weight measurement because they have higher amounts of muscle mass than an average person, and BMI is unable to differentiate between muscle and fat.

Pregnant or lactating women will also show an inaccurate BMI reading.

Children and young people under the age of 18 are also not recommended to use the Body Mass Index because they are still growing.

BMI Pros and Cons

Not everyone agrees that BMI is the best method for weight measurement. Here are the pros and cons to give you a better idea of what you can expect from a BMI weight measurement.


  • Most popular weight measurement tool
  • Easy to calculate
  • Results are consistent and reputable
  • Correlates with other independent body fatness measurements


  • Does not represent body composition or fitness level
  • Does not consider where fat is located
  • Does not differentiate between fat and muscle mass
  • Not suitable for athletes, pregnant women or children

Other Forms of Weight Measurement

There are other ways to measure your weight other than BMI. These types of weight measurement can either be applied on their own or combined with BMI to provide a more accurate picture of your weight.

A waist measurement is another worthwhile option to measure your weight. If a woman has a waist measurement of 80cm or more, or a man has a waist measurement of 94cm or more, this is considered to be overweight.

A waist-to-height ratio is another recommended method of measurement. In this measurement, your waist circumference should not exceed half of your height.

BMI and Weight Loss Surgery

BMI is a necessary tool used to identify if a patient is an appropriate candidate for weight loss surgery. BMI also plays a significant role in helping to determine the type of surgery recommended for a patient.

To be eligible for weight loss surgery, a patient needs to have:

  • A BMI of at least 40, or;
  • A BMI of over 35 and suffering from at least one serious health concern related to obesity

Enter your details into our BMI Calculator to see if you fall under this category. If you think you fit the specifications and wish to explore weight loss surgery options with us at Lap Surgery Brisbane, contact us today.