BMI Calculator

Body Mass Index

Body Mass Index, or BMI, provides a quick snapshot of your weight, helping you to determine if you are a healthy size. BMI is a relative measure of your weight according to your height, and gives you a broad indication of your ideal weight range. You can then use this information to determine how much you should lose to reach a healthy (or healthier) weight.

American Lifestyle and Fitness can help you reach this goal with a personalised diet and exercise plan. We’ll give you all the information, resources and support you need to lower your BMI and get the body you want- quickly and healthily.

Calculate your BMI now and find out how we can help you to look and feel your best!

BMI Calculator (Metric)

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Remember that your BMI should only be used as a general rule as there may be reasons affecting your result. BMI can misleading for:

  1. BMI for Athletes: Some athletes such a body builders have a high BMI due to their high muscle mass, which weighs more than fat.The calculation is only based on weight and height and as such assumes additional weight is through fat.
  2. BMI for Children: In childrenbody fatness changes over the years as they grow, and also differs in girls and boys as they mature. For children is better to compare them to others of similar age and sex.
  3. BMI for Ethnic Groups: BMI values can vary significantly for different ethnic groups. For instance; Chinese, Indian and Malaysian people, are regarded as overweight with a BMI greater than 23 and obese when greater than 27.5.

What is the BMI Calculation?

BMI = weight (kg) / height (m2)

Our BMI calculator does this calculation, so to work out you BMI, you only need to fill out the box above. Your BMI is not an indication of your fat percent but rather just an indication of your weight for your height.

The BMI measurement can often be misinterpreted.It was meant to be a way to classify sedentary (physically inactive) individuals, with average body shapes.However, for these individuals the BMI values can be interpreted as follows: a BMI of 18.5 to 25 indicates optimal weight; a BMI lower than 18.5 indicates being under weight and a BMI above 25 incates being overweight.On the extremes, a BMI below 17.5 demonstrates the person may have anorexia or similar eating disorder and a BMI above 30 is an indication of obesity.

The BMI calculator does not take into consideration age, as mentioned above.For children BMI should be compared to other children of the same age.BMI results are often different between the sexes as well.For instances girls from the age of 12 – 16 tend to have higher BMI’s than boys of the same age.

Though BMI can be calculated quickly and without expensive equipment, it does not take into account many factors, such as frame size and muscularity. Other factors BMI does not consider includes proportions of fat, bone, cartilage and water weight.

As an alternative to our BMI calculator, we also have weight charts which are based on frame size, and can be a better guide to the ideal weight based on height.

what is the bmi calculation

Is there a better healthy weight measurement than BMI?

The Body Mass Index (BMI) measurement has been around for nearly 100 years, and used by the likes of doctors, insurance agencies and weight loss clubs across the globe.However, last week a new study was released from Imperial College, London and the German Institute of Nutrition which showed a large waistline can increase the risk of premature death, even for those people in the healthy BMI range.

Research has shown that every 2 inch increase in waste size causes a 17% increase in the risk of dying for men. BMI focuses on the overall weight based on height, however these latest findings are showing that weight around the waist is more import than overall weight or BMI measurement.

Over 350,000 people took part in this study, over 9 countries and for a period of 10 years.Dr David Haslam, clinical director of the National Obesity Forum, confirms the importance of waist size, by commenting that “abdominal fat is like a giant gland secreting hormones and toxic chemicals that contain inflammatory agents that act on the liver, bowel and arteries to the heart”.In this way, waist measurement may be more important than BMI, given people can still carry significant fat around their waist, yet still have a healthy BMI.

The study found that men whose waists exceed 47in, had a risk of death twice as high compared to those under 31.5in.The same was found for women over 39in compared to those under 25.5in.

Interestingly the study also highlighted our shifting views on weight.In 1999, of the people who had a BMI in the overweight range, over four fifths recognised they were overweight.However in 2007, only three quarters realised they were overweight, based on their BMI.This shows that whether it’s by a BMI calculator or waist measurement, we are slowly becoming desensitised to weight gain and exposing ourselves to health risks.

If BMI is not the best measurement, what waist measurement should you aim for?Well the risk of health problems are increased for measurements greater than 37in for men and 31.5in for women, and substantially increased if greater than 40in for men and 34.5in for women.

Am I Overweight?

Increased body fat has been strongly linked to many diseases, such as high blood pressure, coronary artery disease, stroke, osteoarthritis, some cancers, and type 2 diabetes.

Therefore, being weight conscientious and aware of the dangers is a sensible step towards a healthier, longer life. There are several ways you can measure if you are overweight. Current weight measuring tools as the body mass index, or BMI and waist circumference are amongst the most common used today.


A BMI calculator does this quickly and efficiently. BMI calculators just ask for your height and weight measurements and do the rest for you. Therefore, the higher your BMI score, the higher your risks of disease risks. While a BMI calculator is easy to use, BMI may not be accurate as a true estimation of total body fat as it does not show the difference between fat and muscle. Fat distribution is also important.

BMI Calculator for Women, Men and Kids

BMI Calculator (Imperial)

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Waist Circumference

A waist measurement interrelates with BMI, but also is an independent predictor of risk besides that of BMI. It is not only how much total body fat that affects health, but the location of fat on your body. Studies have found that too much body fat around the stomach region (apple shape) also puts you at higher risk of developing some of these diseases, than if you carry it around the hips and thighs (pear shape). Even if your BMI is at a healthy range, if your waist measurement is more than 89 cm in women, and more than 102 cm in men, you could also be at risk of diseases.

To determine waist circumference, locate the upper hip bone and place a tape measure around the waist (ensuring that the tape measure is parallel to the floor) while standing. Be sure that the tape is snug, but does not compress your skin. Relax your abdomen while measuring your waist and record your measurement.

Waist to Hip Ratio

Similar to the waist circumference is the waist to hip ratio, where both the waist and hip circumference are measured and the score used as an indicator of risk.In contrast to BMI, studies have shown that this provides an effective predictor as it is less dependent on body size and height. Measure your waist at the narrowest part of your body while exhaling, and your hips at the position where the buttocks is maximally extended, when viewed from the side.

This can be calculated by: waist (cm) / Hips (cm)

Scores > 0.80 in women or > 0.90 in men increase chances of diseases, especially cardiovascular disease.

Body Fat Percentage

A common goal is to reduce the amount of total body fat and increase lean muscle tissue for health, performance and aesthetic reasons. Body fat percentage is the total amount of body fat mass in relation to the total body weight conveyed as a percentage.Body fat % is essentially what BMI is trying to broadly estimate.

A healthy body fat range for males is about 9-20% and females 22-32 %.

Body fat percentage (%) = {Body Fat Mass / Body weight} x 100

Again, there is a range of ways to measure total body fat from simple to complex methods. An increasingly popular method has been the body fat analyser. This provides you with your specific body fat percentage and body weight.It measures body fat using Bio-electric Impedance Analysis (BIA). A very low power current is passed through the body, and makes an assessment based on the level of water content in the body (muscle holds a high water content whilst fat holds low content). Callipers are more for professional use and rely very much on the actual tester.Calipers test for skin fold measurements and extrapolate this out to estimate body fat %.

Height-Weight & Frame Charts

On of the big drawback of BMI is not taking into account frame size.Frame charts can facilitate in establishing a more realistic weight range, and taking into account your frame size.You can measure your frame size by placing your index finger around your wrist and linking it with your thumb.

Small Frame = index finger partly covers thumb.

Medium Frame = index finger and thumb meet.

Large Frame = there is a gap between index finger and thumb, they do not meet.


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