Image copyright Getty Images Image caption Knowing your weight and height is enough to calculate your body mass index

You've been using our fat calculator in your droves, working out your BMI (body mass index) and comparing the result with people in your age group and your part of the UK.

But a few people have been critical. They say using BMI to measure whether they are healthy, overweight or obese is misleading.

So what's the truth? Can we trust what it tells us?

Is BMI the best measure of obesity?

Firstly, it is a quick and easy way of working out whether you are in the healthy category by using two simple measures - weight and height.

Most doctors say it is the best method they have, it's pretty accurate, can be measured simply in clinic and is acceptable to patients.

"It works in the vast majority of people, the vast majority of time," says Prof Naveed Sattar, from the University of Glasgow.

"If two people are the same height and one has a BMI of 25 and the other a BMI of 40, then excess body fat is the reason."

Measuring BMI is also much more accurate and potentially less embarrassing than measuring someone's waist circumference, which is also a good guide.

BMI is calculated by dividing an adult's weight by the square of their height.

Your browser does not support this lookup. Cannot retrieve data. Height cm Feet in cm ft/in Weight kg stone lb kg st/lb Age Age Gender Female Male Postcode Postcode Region Please choose Scotland Wales Northern Ireland the North East the North West the East Midlands the West Midlands Yorkshire and the Humber the East of England London the South East the South West Region Waist size (optional) i To measure your waist, find the bottom of your ribs and the top of your hips and wrap a tape measure midway between these points. Breathe out naturally before taking the measurement. Waist size (optional) Waist size (optional) cm in See how you compare Your BMI Your BMI is [bmi_result] which is in the [bmi_category] category. Healthy Overweight Obese Very obese Underweight 30 40 18.5 25 Healthy Overweight Obese Very obese Under- weight 30 40 18.5 25 BMI is a standard way of measuring if people are a healthy weight for their height. For most adults 18.5 to 24.9 is the healthy range. Your age group Your BMI is [comparative] the average of [bmi_score] for a [gender_singular] in your age group ([user_age_group]) in [user_country]. About [percent]% of [gender_plural] in your age group in [user_country] are overweight, obese or very obese. 0% Underweight 0% Healthy 0% Overweight 0% Obese 0% Very obese Your part of the UK In all parts of the UK, the majority of the adult population is overweight, obese or very obese, according to the latest national surveys. In [region], the figure is about [percentage]% of [gender_plural]. North East 50% West Mids 50% Scotland 50% East Mids 50% Yorks & Humb 50% N. Ireland 50% North West 50% South East 50% South West 50% East 50% Wales 50% London 50% 50% What does this mean for you? The information you've given us indicates you could be underweight. There can be health risks associated with a low BMI such as anaemia, osteoporosis, a weakened immune system and fertility problems. This is not a medical diagnostic tool so don't panic if this isn't the result you were expecting to see. If you're concerned about your weight, or your health in general, speak to a healthcare professional such as your GP. You're in the healthy range which is great. Research shows that having a healthy BMI can reduce your risk of serious health problems, such as type 2 diabetes, heart disease, stroke and some cancers. But not all people with a BMI in this range have a lower risk. Other factors such as smoking, high blood cholesterol or high blood pressure will increase your risk. If you're of Asian descent you have a higher risk of heart disease and diabetes at a lower BMI and waist circumference. A healthy BMI for you would be 18.5-23. We're more likely to gain weight as we get older so to stay a healthy weight you may need to make small changes to your diet or your activity levels as you age. The information you've given us indicates you are overweight. Research shows that a BMI above the healthy range can increase your risk of serious health problems, such as type 2 diabetes, heart disease, stroke, and some cancers. A healthy BMI for a person of your height would be 18.5-24.9. If you're of Asian descent you have a higher risk of heart disease and diabetes at a lower BMI and waist circumference. A healthy BMI for you would be 18.5-23. Losing even a small amount of weight, if sustained, can have a big impact. For most people changing your diet is by far the best way to lose weight. Activity can help you maintain your target weight, and can have other health benefits, but increasing activity alone is not nearly as effective as diet at helping you shed the pounds. Even small changes like reducing portion sizes or choosing lower calorie snacks and drinks can help you lose weight or stop putting it on. The information you've given us indicates you're in the obese category. Research shows that having a BMI in this range will significantly increase your risk of serious health problems, such as type 2 diabetes, heart disease, stroke, and some cancers. A healthy BMI for a person of your height would be 18.5-24.9. If you're of Asian descent you have a higher risk of heart disease and diabetes at a lower BMI and waist circumference. A healthy BMI for you would be 18.5-23. Losing even a small amount of weight, if sustained, can have a big impact. For most people changing your diet is by far the best way to lose weight. Activity can help you maintain your target weight, and can have other health benefits, but increasing activity alone is not nearly as effective as diet at helping you shed the pounds. There's lots of support available to help you make changes, either to lose weight or to stop putting on weight. The information you've given us indicates you're in the very obese category. Research shows that having a BMI in this range will significantly increase your risk of serious health problems, such as type 2 diabetes, heart disease, stroke, and some cancers. A healthy BMI for a person of your height would be 18.5-24.9. If you're of Asian descent you have a higher risk of heart disease and diabetes at a lower BMI and waist circumference. A healthy BMI for you would be 18.5-23. Losing even a small amount of weight, if sustained, can have a big impact. For most people changing your diet is by far the best way to lose weight. Activity can help you maintain your target weight, and can have other health benefits, but increasing activity alone is not nearly as effective as diet at helping you shed the pounds. If you are concerned, or would like to find out more, speak to your doctor or GP. If you are ready to make lifestyle changes, there is lots of support available. Your waist size BMI is not the only way of measuring whether you are a healthy weight. Doctors say that carrying too much fat around your belly can increase your risk of health problems. Excess fat in this area can stress internal organs - even if your BMI is in the healthy range. Your waist size is [size] For [gender_plural], the NHS says a waist size of: 80cm (31.5 inches) or more means an increased risk of health problems 88cm (34 inches) or more means a very high risk of health problems 94cm (37 inches) or more means an increased risk of health problems 102cm (40 inches) or more means a very high risk of health problems People from non-white ethnic groups may be at risk at a lower waist size How to check your waist with just a piece of string

If you can't see the calculator tap or click here.

But does it work for everyone?

No, not all.

And this provoked a few comments along these lines: "Why, in this day and age, are you using BMI to tell people they are overweight? It is an outdated method that does not take into consideration muscle and actual health! I am extremely fit and healthy with a low body fat percentage, yet your BMI tells me (and many more self-conscious girls) that I am overweight!"

There are some people who carry a lot of muscle and little fat, like bodybuilders, boxers and rugby players.

Muscle is much denser than fat so they may end up with a BMI that classes them as obese, despite the fact they may be fit and healthy.

Image copyright Getty Images Image caption Some professional rugby players will be classed as obese because of their high muscle mass - but this is rare

But this is thought to apply to fewer than 1% of the population. Most people aren't extreme athletes.

Tim Cole, professor of medical statistics, at University College London Great Ormond Street Institute of Child Health, said BMI was "still extremely relevant".

"You don't see many bodybuilders around but you do see lots of people with large waists. Many people get exercised about that wrongly."

As people age, they lose muscle and may be classed in the "healthy weight" range even though they may be carrying excess fat. This is particularly true of smokers.

BMI also doesn't apply to pregnant women, and some ethnic groups have a higher risk of health problems at lower BMI levels.

Does BMI actually measure fat?

It can't measure how much excess fat we have in our bodies - as opposed to muscle and bone - because that would require some pretty complicated and expensive medical procedures, which just aren't practical to carry out on the whole population.

What it does do is give a healthy weight range for a particular height, taking into account variations in body shape - and it provides a good starting point for the majority of people.

It also doesn't measure how fat is distributed throughout the body (some fat is ok; too much in the wrong place is a risk).

Research shows that people who carry a lot of fat around their waists are at higher risk of health problems than those with more fat around their thighs and buttocks.

They are more likely to have fat stored in their abdomen around key organs, which could increase the risk of heart disease, stroke and type 2 diabetes.

So waist size may be a better way to monitor your health than BMI. That's why our calculator included an option for giving your waist size too.

"If people think they have lots of muscle mass, their waists should be lower for a given BMI - so they can easily check," says Prof Sattar.

Image copyright Getty Images

How to measure your waist

find the bottom of your ribs and the top of your hips

wrap a tape measure around your waist midway between these points

breathe out naturally before taking the measurement

Regardless of your height or BMI, you should try to lose weight if your waist is:

men - 94cm (37ins) or more

women - 80cm (31.5ins) or more

Can BMI tell us anything about disease risk?

On its own, it can't.

But doctors use BMI in conjunction with other measures - like blood pressure, cholesterol and family history - to work out an individual's risk of type 2 diabetes or heart disease, for example.

Body mass index is not specific to any particular health risk - and that's its strength, experts say.

However, a BMI above the healthy range or too much fat around the waist is known to increase the risk of serious health problems, including stroke and certain cancers.

Are we shaming those who are overweight?

One person said of the BBC calculator: "Your unscientific method of calculating 'fatness' is an unhelpful tool that dehumanises those who are obese or overweight, shaming them into losing weight and threatening their fragile relationship with their bodies."

There was no intention of shaming people - merely offering a way of finding out about your own weight because excess fat is the cause of an increased risk of a range of diseases.

If you think you would like to lose some weight, you should go and see your GP for advice first.

The best way to lose weight is to make small, realistic changes to your diet and physical activity.