Body Roundness Index (BRI) Calculator
This calculator gives an informational estimate only. BRI describes an association observed across populations. It does not predict what will happen to you or diagnose anything. Discuss an elevated result, or any measurement you are unsure about, with your GP.
What Body Roundness Index measures
Body Mass Index has one blind spot that everybody knows about: it cannot tell muscle from fat, and it has no idea where on your body that fat sits. Body Roundness Index was built to answer the second half of that.
The method is geometric. It treats your body as an ellipse as tall as you are and as wide as your waist divided by pi, then measures how round that ellipse is. A long, narrow ellipse scores low. A rounder one scores higher. Your weight never enters the calculation, so the number is describing your proportions rather than your mass.
It was published in 2013 by Diana Thomas and colleagues, who derived and validated it against DXA and MRI body composition scans.
The reason it has drawn attention since is that it correlates more closely with visceral fat, the fat that sits deep around the abdominal organs, than height and weight alone can.
What is a good BRI score?
Most BRI calculators score your result against bands taken from a large American mortality study. We do not, and the reason is worth understanding before you compare our number to anyone else’s.
The Australian thresholds
Australia has published waist thresholds. The National Health and Medical Research Council guidance, as reported by the Australian Institute of Health and Welfare, associates a waist above 80cm in women and 94cm in men with increased risk of chronic conditions, and above 88cm and 102cm with substantially increased risk. Those numbers are what your GP works from.
Bands built from your measurements
So this calculator converts those thresholds into BRI at your own height, and those become your bands. Someone 165cm tall and someone 185cm tall are being measured against the same waist guidance, but it lands at a different BRI for each of them. That is why the scale in your result is built from your measurements rather than pulled from a fixed table.
Australian guidance uses lower waist thresholds for people of Asian, Aboriginal or Torres Strait Islander descent, following the approach taken by the Australian Type 2 Diabetes Risk Assessment Tool. The calculator has a toggle for this.
The thresholds are converted at your height rather than copied from a fixed BRI table.
Why height changes the scale
The same waist measurement can produce a different BRI at different heights. That is why the result is personal to the measurements you enter.
Adjusted guidance
Lower waist thresholds apply to people of Asian, Aboriginal or Torres Strait Islander descent, following Australian risk-assessment guidance.
What to do with a borderline result
A result close to a threshold is not meaningfully different from one just across it. Repeat the measurement carefully and discuss anything you are unsure about with your GP.
Why BRI charts disagree with each other
The bands almost every BRI tool uses come from a 2024 study in JAMA Network Open that followed just under 33,000 American adults for a median of ten years. It found the lowest all-cause mortality in the middle fifth of the population, a BRI of 4.5 to 5.5, with raised mortality below 3.4 and at 6.9 or above. It is a good study. It is the wrong scale to score an Australian against. Read the table below to see why. The same study recorded average American BRI climbing from 4.8 to 5.6 between 1999 and 2018. The middle moved because the population moved. The low end deserves its own caution: raised mortality among the leanest group in a cohort study commonly reflects illness-related weight loss rather than leanness itself, which is why we do not tell anyone their BRI is too low.
Australian waist thresholds, expressed as BRI
The same waist guidance lands at a different BRI at different heights. These values show the thresholds used to score your result.
155cm
3.67
4.72
5.57
6.81
160cm
3.36
4.34
5.15
6.30
165cm
3.08
4.01
4.76
5.85
170cm
2.82
3.70
4.41
5.43
175cm
2.59
3.41
4.08
5.05
180cm
2.38
3.15
3.79
4.70
185cm
2.18
2.91
3.51
4.37
190cm
2.00
2.69
3.26
4.08
Read the 180cm row. A man with a 102cm waist, which Australian guidance places at substantially increased risk, computes to a BRI of 4.70. On the American scale that sits inside the band with the lowest recorded mortality. Run it the other way and a 180cm man needs a waist between roughly 100cm and 109cm to reach that band at all.
Now read the women’s columns. A woman at or under the 80cm Australian threshold computes below 3.4 at every height from 165cm upward, which the American scale flags as the elevated-risk low tail.
BRI vs BMI, and what a disagreement means
Entering your weight is optional. If you do, the calculator works out your BMI as well, and the useful output is not the second number. It is whether the two measures agree.
There is a common claim that BMI is broken. It is overstated. A 2025 analysis of more than 2,000 adults found that of those classified obese by BMI alone, 98% also met obesity criteria on a second measure such as BRI or a direct body composition scan. When BMI raises its hand, it is usually right.
The problem is the other direction. BMI is reliable when it flags you and unreliable when it clears you.
BMI and waist both sit below their thresholds
The measures agree, and there is less that either is hiding.
Both sit above
The measures agree, and this is the case where BMI on its own was already reliable.
BMI is above the healthy range but waist is not
BMI cannot separate muscle from fat, so a muscular or heavier-framed build reads as overweight on BMI alone while the waist-based measures do not flag.
BMI is in the healthy range but waist is above the threshold
This is the one BMI alone does not catch, and it is the reason this calculator asks for a waist measurement at all.
None of these is a diagnosis, and none of them is about your weight. What they can tell you is whether it is worth looking at what is happening metabolically, which needs a blood test rather than a tape measure.
The useful takeaway
Retest with the same method over time. Consistency makes the trend meaningful.
TAKE CONTROL OF YOUR HEALTH
A result is a prompt to look more closely, not a conclusion.
Limitations of the Body Roundness Index
It is a screening prompt, not a test. BRI describes an association observed across populations. It does not predict what will happen to you, and it does not diagnose anything.
It cannot see inside you. Two people with the same BRI can have very different blood pressure, blood glucose, cholesterol and liver function. Body shape is correlated with those things, not a substitute for measuring them.
There is no Australian BRI reference data. No published dataset describes how BRI is distributed across the Australian population. That is precisely why this calculator scores against waist thresholds, which Australia has published, rather than against BRI norms, which it has not.
It is less useful at the extremes of build. Very muscular people and people who are pregnant will get results that do not mean what the model assumes. The same applies to anyone with significant abdominal swelling from a medical cause.
Waist thresholds are population-level. They were derived to identify groups at higher risk, not to draw a line through individuals. A result a centimetre either side of a threshold is not meaningfully different from one on the other side.
Reviewed by a practising clinician. As with every calculator on this site, the method, thresholds and result copy have been reviewed before publication.
How to measure your waist correctly
How to measure your waist
The BRI formula is arithmetic. It introduces no uncertainty of its own, which means every bit of error in your result comes from how you measured. Moving the tape two centimetres changes BRI by roughly 0.1 to 0.15, which is enough to cross a threshold if you are near one. The calculator will tell you when your result is close to a line, because at that point the honest answer is that the measurement cannot separate you from it.
Stand relaxed, without holding your stomach in. Measure at the level of your navel, with the tape horizontal and level all the way around. Breathe out normally and take the reading at the end of that breath. Keep the tape snug against the skin without compressing it. Use the tape measurement rather than the waist size printed on your trousers, and if you track this over time, measure at the same time of day, ideally in the morning before eating.
Sources
The BRI method
Obesity
Body Roundness Index and its relationship with body composition.
https://onlinelibrary.wiley.com/doi/10.1002/oby.20408JAMA Network Open
BRI bands and all-cause mortality in American adults.
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2819674Australian Institute of Health and Welfare
Waist circumference and chronic disease risk in Australia.
https://www.aihw.gov.au/reports/diabetes/diabetes/contents/diabetes-risk-factors/waist-circumference
Additional guidance
National Health and Medical Research Council
Australian guidance on waist thresholds.
https://www.nhmrc.gov.auAustralian Type 2 Diabetes Risk Assessment Tool
Lower thresholds for some populations.
https://www.health.gov.au
FAQs
