BMI Calculator

Calculate your BMI (Body Mass Index)

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BMI Calculator

Your Body Mass Index (BMI) is an estimated measure of your body fatness that is based on your height and your weight. While it does not provide a full picture of your health (as will be discussed below), it can be a basic gauge to understand whether you are at a healthy weight. Your GP will likely use your BMI to help determine if you are at risk for certain health problems. 

How to Use This Calculator

Our calculator employs the use of the standard BMI formula which produces a result using your individual height and weight that you must input into the calculator in either metric or imperial units. The BMI calculation will provide you with a score that will categorise you as either underweight, normal weight, overweight or obese, and wil also provide a desirable weight range for your individual height. Even if your goal is not weight-related, the BMI calculator provides a consistent assessment of health risks for the general public.

What Is BMI?

Your BMI is a measure of the ratio of your height to your weight which provides an estimation of body fatness.  It does not directly measure body fat, rather it gives an indication of excess body weight and helps to determine if you are in a healthy or unhealthy weight range. A high BMI can indicate too much body fat, whereas a low BMI can indicate too little body fat.

Having a higher BMI is associated with an elevated risk of developing obesity related chronic diseases such as type 2 diabetes, high blood pressure, and cardiovascular disease (1, 2, 3). Likewise, a BMI too low can elevate the risk of developing health issues such as bone loss (osteoporosis) and increased susceptibility to illness due to lowered immune function (4, 5).

How Is BMI Used?

BMI screening is an important health indicator which is widely used by health professionals since it is an inexpensive, straightforward method, which makes it a popular initial stage of most health examinations relating to body weight issues. Based on estimation, it is used to identify whether an individual has an abnormal body weight in relation to their height. While it gives a general picture of whether an individual is carrying excess body weight,it is not a reliable measure of an individual's body fat. Other relatively easy methods can be used to evaluate body fat, alone or combined with BMI, such as waist to height ratio, skinfold thickness, waist circumference, and bioelectrical impedance analysis (6).

Other more advanced testing methods with a greater accuracy include computed Tomography (CT scan), dual-energy x-ray absorptiometry (DeXA scan) and magnetic resonance imaging (MRI scan) (7). However, these tests are more costly and more often than not difficult to access, making them impractical for use in a clinical setting.

How to Work Out BMI?

Body Mass Index is a relatively simple calculation that determines an individual’s height to weight ratio. BMI calculations divide a person’s weight in kilograms by their height in metres squared. For example, if an individual weighs 70kg and is 1.8m tall, the following calculation would be performed: 70/1.8² = BMI of 22. This can be shown as 22kg/m2.

The standard weight status categories by which adults can interpret their BMI are as follows:

A BMI below 18.5 –underweight range
A BMI between 18.5 and 24.9 –healthy weight range
A BMI between 25 and 29.9 –overweight range
A BMI above 30  –obese range

These ranges used are the same regardless of differences in gender, age and body shape.

BMI Chart

The following is a BMI chart that can help you to understand where your BMI falls in relation to others’.       

Sourced from:

  • What is a healthy BMI?
    A healthy adult BMI is considered to be in the range between 18.5 and 24.9. However, it is important to remember that this value is only an estimate - there are many factors that may mean you score outside of his range, such as age or gender. Generally speaking, if your BMI sits within this range, you will be at a lower risk of developing chronic diseases such as type 2 diabetes and cardiovascular disease (8).

  • What is an unhealthy BMI?
    An unhealthy adult BMI is considered any score that sits outside of the healthy BMI range (18.5-24.9). A BMI below 18.5 is considered underweight, while a BMI above 25 is considered overweight. A BMI above 30 is considered obese, between 35 - 40 is severely obese, and above 40 is considered morbidly obese. According to the latest World Health Organisation (WHO) statistics from 2016, over 1.9 billion adults are considered overweight (approximately 39% of the global adult population, of whom 650 million are considered obese (approximately 13% of the global adult population)(9).

What Are the Limitations Of BMI?

While BMI does factor in natural variations of body shape to provide a healthy weight range for certain heights, it is not without limitation. BMI does not provide an accurate reflection of body fat percentage nor location of body fat on the body, both of which are factors that may influence overall health. For example, an individual may have a healthy BMI, despite having a large amount of fat located in the abdominal region (stored around their organs).

Research suggests that individuals carrying alot of fat in this region specifically could be at a greater risk of developing health issues such as metabolic syndrome, in comparison to those with fat distributed in other areas of their body (10).

Therefore, using BMI alone only provides one piece of the puzzle. You will find your BMI information even more helpful when paired with your body fat ratio – use a Body Fat Calculator to find this information.

BMI also does not distinguish between muscle mass, fat and bone, therefore, an individual may be given a high BMI result despite having a very low level of body fat; conversely, an individual may be given a low BMI result despite having very high body fat levels (11, 12). As a result, you can change your body composition while your BMI stays the same (13). For instance, you may lose body fat but gain muscle mass due to weight training.

This is because body composition may vary massively from one individual to the next. Muscle has a greater density than fat (1.06kg/L vs. 0.9kg/L)(14, 15), and therefore weighs more, which can influence an individual’s interpretation of the BMI result. For example, very muscular individuals such as athletes or weight trainers (either recreational or competitive) may be classified as overweight or obese according to their BMI calculation, despite being at a healthy body weight. Similarly, older adults that have experienced muscle mass loss due to increasing age may be classified as a healthy weight, despite having excess body fat and being overweight.

In this case, other additional anthropometric measurements to assess body fat percentage may be used by a health professional that are clinically relevant, such as skinfold thickness.

Certain ethnic groups may also need further assessment. For example, adults from most Asian ethnicities could experience a greater risk of developing health problems, including high blood pressure and cardiovascular disease, despite having a BMI that is lower than 25 (healthy weight) (16, 17).

BMI is not designed to be used if you are pregnant. If you are pregnant and are concerned that your body weight is too high or too low, consult your midwife or GP for advice. Another factor that BMI does not take into account is gender. Women typically store larger amounts of body fat than men at an equal BMI.

Using BMI for your health journey

Once you are armed with knowledge about your BMI, you can use this information on your health journey. If you have fallen into the ‘healthy’ weight range, you can still consider improving your strength and muscle mass. If you are classified as underweight, you should consult with your GP and/or a qualified dietician to develop a strategy for weight gain, if determined to be necessary.

If you are in the overweight or obese category, consult with your GP and/or a  qualified dietician to find out if you should begin a weight loss journey. There is no ‘easy fix’ to weight loss – it takes time, dedication, will power, and effort.

Being at a healthy weight is key to living a good quality of life. It is clear that the underpinning principle for maintaining a healthy weight or losing weight is calorie balance, that being “calories in versus calories out”, and this can be manipulated by changing how much you eat or how much you move, or both. However, there are many other factors also at play to consider to ensure that this is achieved and adhered to in the long term, whilst also supporting overall health, including macronutrient quantities (e.g. high protein intake), satiety (hunger and feelings of fullness), diet variety, and nutrient density of foods.

Remember, while BMI (body weight) is an important indicator for health risk, it is not the only determinant for optimal health.

Use a Macro Calculator to ensure that you are eating the right percentage of fat, carbs, and protein.

When it comes to exercise, you have to find something that you enjoy doing, otherwise, you likely won’t stick with it over the long haul. Think outside the box – swimming, surfing, skateboarding, and cycling are all fun and energetic ways to burn calories, get fit, and boost your endorphins.

Building muscle is a smart idea, as people with a higher percentage of muscle mass burn more calories, even when they are at rest. Use a 1 Rep Max Calculator to find your limit, and then you can take your exercise routine right up to your natural edge. Before you know it, you will be blasting past your old personal bests, building muscle, and lowering your BMI.

No matter which plan you use to eat healthier and get more exercise, the journey starts here!


1. Guh, D., Zhang, W., Bansback, N., Amarsi, Z., Birmingham, C. & Anis, A. (2009) The incidence of co-morbidities related to obesity and overweight: A systematic review and meta-analysis. BMC Public Health, 9 (1).

2. Bogers, R. P., Bemelmans, W. J., Hoogenveen, R. T., Boshuizen, H. C., Woodward, M., Knekt, P., van Dam, R. M., Hu, F. B., Visscher, T. L., Menotti, A., Thorpe, R. J., Jr, Jamrozik, K., Calling, S., Strand, B. H., Shipley, M. J., & BMI-CHD Collaboration Investigators (2007). Association of overweight with increased risk of coronary heart disease partly independent of blood pressure and cholesterol levels: a meta-analysis of 21 cohort studies including more than 300 000 persons. Archives of internal medicine, 167(16), 1720–1728.

3. Strazzullo, P., D'Elia, L., Cairella, G., Garbagnati, F., Cappuccio, F. & Scalfi, L. (2010) Excess Body Weight and Incidence of Stroke. Stroke, 41 (5).

4.Dobner, J. & Kaser, S. (2018) Body mass index and the risk of infection - from underweight to obesity. Clinical Microbiology and Infection, 24 (1), pp.24-28.

5. Lim, J. & Park, H. (2016) Relationship between underweight, bone mineral density and skeletal muscle index in premenopausal Korean women. International Journal of Clinical Practice, 70 (6), pp.462-468.

6. Ozhan, H., Alemdar, R., Caglar, O., Ordu, S., Kaya, A., Albayrak, S., Turker, Y. & Bulur, S. (2012) Performance of Bioelectrical Impedance Analysis in the Diagnosis of Metabolic Syndrome. Journal of Investigative Medicine, 60 (3), pp.587-591.

7. Wang, H., Chen, Y. & Eitzman, D. (2014) Imaging body fat: techniques and cardiometabolic implications. Arteriosclerosis, Thrombosis, and Vascular Biology, 34 (10), pp.2217-2223.

8. Field, A., Coakley, E., Must, A., Spadano, J., Laird, N., Dietz, W., Rimm, E. & Colditz, G. (2001) Impact of Overweight on the Risk of Developing Common Chronic Diseases During a 10-Year Period. Archives of Internal Medicine, 161 (13), p.1581.

9. World Health Organization (2020) Obesity and overweight [Internet]. Available from: <>.

10. Kwon, H., Kim, D. & Kim, J. (2017) Body Fat Distribution and the Risk of Incident Metabolic Syndrome: A Longitudinal Cohort Study. Scientific Reports, 7 (1).

11. Strain, G. & Zumoff, B. (1992) The relationship of weight-height indices of obesity to body fat content. Journal of the American College of Nutrition, 11 (6), pp.715-718.

12. Flegal, K., Shepherd, J., Looker, A., Graubard, B., Borrud, L., Ogden, C., Harris, T., Everhart, J. & Schenker, N. (2008) Comparisons of percentage body fat, body mass index, waist circumference, and waist-stature ratio in adults. The American Journal of Clinical Nutrition, 89 (2), pp.500-508.

13. Barbeau, P., Gutin, B., Litaker, M., Owens, S., Riggs, S. & Okuyama, T. (1999) Correlates of individual differences in body-composition changes resulting from physical training in obese children. The American Journal of Clinical Nutrition, 69 (4), pp.705-711.

14. Urbanchek, M., Picken, E., Kalliainen, L. & Kuzon, W. (2001) Specific Force Deficit in Skeletal Muscles of Old Rats Is Partially Explained by the Existence of Denervated Muscle Fibers. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 56 (5), pp.B191-B197.

15. Farvid, M., Ng, T., Chan, D., Barrett, P. & Watts, G. (2005) Association of adiponectin and resistin with adipose tissue compartments, insulin resistance and dyslipidaemia. Diabetes, Obesity and Metabolism, 7 (4), pp.406-413.

16. Deurenberg-Yap, M., Chew, S. & Deurenberg, P. (2002) Elevated body fat percentage and cardiovascular risks at low body mass index levels among Singaporean Chinese, Malays and Indians. Obesity Reviews, 3 (3), pp.209-215.

17. Wulan, S., Westerterp, K. & Plasqui, G. (2010) Ethnic differences in body composition and the associated metabolic profile: A comparative study between Asians and Caucasians. Maturitas, 65 (4), pp.315-319.

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