Welcome to our Body Mass Index (BMI) calculator.
BMI is a general indicator of whether or not someone is a healthy weight relative to their height.
Our calculator shows you your BMI, your BMI health category, where you fall on the BMI scale, and your healthy weight range.
Whilst BMI can be a very useful metric, it is important to understand its limitations, so scroll below the calculator to get a detailed breakdown of what exactly BMI is, and what exactly it does and doesn’t tell you.
BMI Calculator
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obesity Class 1 | 30 – 34.9 |
| Obesity Class 2 | 35 – 39.9 |
| Obesity Class 3 | 40 and Above |
*Please note that the BMI categories for Black, Asian, and some other minority ethnic groups are slightly different from those above. Keep scrolling to view these differences.
Want to visualize BMI further? - Jump to BMI healthy weight charts.
The Honest Truth: Why BMI Lies to Most Runners
BMI is a screening tool that was never designed to assess individual health, and it’s especially noisy for the population most likely to be on this page: regular runners. Before you take a number from the calculator above and treat it as a verdict, here’s what the body-composition literature actually says about it.
1. BMI was built for populations, not individuals
The Quetelet Index — what we now call BMI — was developed in 1832 to characterise the average build of a population, not to diagnose any individual. The category cut-offs of 18.5, 25, and 30 came from large-scale insurance and epidemiology data in mostly European cohorts, where they correlated reasonably with all-cause-mortality risk at a group level1Nuttall FQ. Body Mass Index: Obesity, BMI, and Health: A Critical Review. Nutrition Today. 2015;50(3):117–128.. They were never validated to tell a single person whether they’re at a healthy weight. The American Medical Association formally acknowledged this limitation in 2023 and recommended BMI be used alongside (not instead of) measures like waist circumference, body composition, and cardiometabolic blood markers2American Medical Association. AMA adopts new policy clarifying role of BMI as a measure in medicine. Press release; June 14, 2023..
2. It systematically over-classifies muscular runners as overweight
Because BMI uses total body mass and ignores composition, lean muscle counts the same as fat. In studies pairing BMI with DXA-measured body fat in trained runners and triathletes, BMI misclassifies roughly 25–40% of athletic individuals into the "overweight" or "obese" categories despite body-fat percentages well within the healthy range3Romero-Corral A, Somers VK, Sierra-Johnson J, et al. Accuracy of body mass index in diagnosing obesity in the adult general population. International Journal of Obesity. 2008;32(6):959–966.. The shorter and more muscular the runner, the bigger the mis-classification: a 5’4" trained female runner at 130 lb with 18% body fat lands in the same BMI bucket as a 5’4" sedentary individual at 130 lb with 35% body fat, despite hugely different cardiometabolic risk profiles.
3. The healthy ranges are not the same across all ethnicities
The standard 18.5–24.9 "normal" band over-estimates the safe range for runners of South Asian, Chinese, and many other Asian backgrounds. At equal BMI, those populations carry meaningfully more visceral fat and have higher rates of type-2 diabetes and cardiovascular events, which is why the WHO now recommends a lower at-risk threshold of 23 (rather than 25) for South and East Asian populations4WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet. 2004;363(9403):157–163.. Conversely, several studies in athletic Pacific Islander populations show overestimation of risk at the standard cut-offs. If you’re using BMI as one signal, your "normal" band may not be 18.5–25.
4. Waist-to-height ratio is a sharper single number for runners
If you only have time to track one weight-related metric, waist-to-height ratio (WHtR) outperforms BMI for predicting cardiometabolic risk and visceral fat across ethnicities and athletic backgrounds5Ashwell M, Gunn P, Gibson S. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: systematic review and meta-analysis. Obesity Reviews. 2012;13(3):275–286.. The simple rule of thumb — keep your waist below half your height — is more diagnostic for distance runners than any BMI bucket. Track it once a quarter alongside resting heart rate, weekly mileage, and your VO₂max trend, and you’ll have a far more useful health dashboard than BMI alone.
5. Read your BMI as one data point, not a verdict
For someone who isn’t carrying significant muscle and isn’t in an Asian-population subgroup, BMI is still a reasonable rough triage. For runners — especially trained ones, female runners on the lower end of the range, and anyone with notable muscle on the upper end — the calculator above is a starting point, not a diagnosis. Use the result alongside waist measurement, body-fat measurement if you have access to a DXA or smart scale, training load, energy availability, and your resting and running heart-rate trends. The number on its own tells you almost nothing about your performance ceiling or your long-term cardiometabolic risk.
Who Is This Calculator For?
This calculator is for adults, men or women, who want to calculate their BMI. It is not suitable for calculating the BMI of children, as this requires a different equation.
BMI is a useful measurement that can be used to assess whether or not an individual is a healthy weight.
However, if you are worried about your health, please speak to a healthcare professional.
In particular, if you have an eating disorder, the BMI results do not apply, and you should speak to a doctor.
Related: Weight Loss Guides
Related: Diet Guides
Related: Training Guides
What Exactly Is My BMI?: The Body Mass Index Explained
Body mass index or BMI is a measure of your weight compared to your height. It is measured in kg/m2.
BMI is useful, as it can indicate whether or not someone is overweight or obese, conditions which are linked to a higher risk of illnesses such as type-2 diabetes, heart disease, and cancer.
In this way, for most adults, BMI gives a decent estimate as to whether or not they are a healthy weight.
Limitations Of BMI
BMI does not account for muscle mass. Therefore, due to the fact that muscle weighs more than fat, muscular adults can occasionally be incorrectly classified as overweight according to their BMI.
These overestimations tend to occur in the 25-35 BMI range.
On the other end of the spectrum, most of the world's top long-distance runners would be considered underweight according to their BMI, despite them being incredibly healthy in reality.
If you are unsure about your BMI result, you can also measure your waist-to-height ratio, which is an additional indication of healthy body fat. Or, check out our body fat calculator.
No single metric can give an absolute measure of health. Rather than aiming for a specific number on a scale, the most important thing is to maintain a healthy, active lifestyle and a healthy diet.
Related: How Much Should I Walk According To My BMI?
Ethnic Differences In BMI and Disease Risk
It is important to note that the healthy BMI range for Black, Asian, and some other minority ethnic groups is lower.
This is likely due to differences in muscle mass and ways in which fat is stored in the body.
In particular, some research shows that BMI is a weak indicator of weight-related health for those of South Asian ethnicity. Body fat calculation methods such as hip-to-waist ratio or our Body Fat Calculator have been shown to be better indicators of weight-related health among South Asians.
There are disputes as to what exactly the BMI category cutoff points should be for different ethnic groups. Currently, in Japan and China, overweight is defined as a BMI greater than 24, and obesity is defined as greater than 28. In India, overweight is defined as a BMI of greater than 23 or higher, and obesity is defined as 27 or higher.
Amongst white populations, diabetes prevention is needed once individuals are classed as being obese (BMI greater than 30). However, recent studies show that diabetes prevention measures are required at lower BMIs for other ethnicities. The research suggests that diabetes prevention is needed at or above a BMI of:
- 24 in South Asian populations
- 27 in Arab and Chinese populations
- 26 in Black Caribbean populations
- 27 in Black Other populations
- 29 in Black African populations
- just below 30 in Black British populations
BMI Healthy Weight Charts
These BMI healthy weight charts can further help you visualize the Body Mass Index categories.
Click here to download the BMI Chart (Imperial/US) as a PDF.
Click here to download the BMI Chart (Imperial/US) as a PNG image.
Click here to download the BMI Chart (Metric) as a PDF.
Click here to download the BMI Chart (Metric) as a PNG image.
How Is BMI Calculated?
BMI is calculated as your weight in kilograms divided by the square of your height, as outlined in the formula below.
Other Health Calculators
- Body Fat Calculator
- Ideal Body Weight Calculator
- Daily Calories Burned Calculator
- TDEE Calculator
- Calories Burned Per Activity Calculator
- Calories Burned Per Distance Run Calculator
