Image: iStock.

Although it’s not without its critics, the Body Mass Index (BMI) is widely perceived as a valid indicator of whether one’s body fat is a threat to their health. But if you don’t have a set of scales, a measuring tape or a calculator nearby, it can be a bit of a hassle to work out.

However, a new study suggests there’s a more accurate way to determine if you’re an unhealthy size, and all you need is your body and a ball of string.

RELATED: This weight-loss trend is dangerous. And it doesn’t even work.

You simply measure your height with the string — or wool, ribbon, floss, whatever’s handy — then fold it in half and see if it can fit comfortably around your waist. If not, you could be at risk of serious health issues like heart disease. (Post continues after gallery.)

Positive celebrity quotes about diets.

Jennifer Lawrence

Jennifer Lawrence said to Us Weekly, "I like food. I don't really diet or anything. I'm miserable when I'm dieting and I like the way I look. I'm really sick of all these actresses looking like birds."

Beyonce

After losing weight for her role in Dreamgirls, Beyonce said to GMTV, ''The funnest part was putting the weight back on and eating my doughnuts and all the other things, so now I'm back to my body."

Jennifer Aniston

Jennifer Aniston said to Women's Health, "I went from being a crazy workout girl to sort of saying, 'My body wants a little bit a of break.' So I kind of stay with more simple stuff and taking walks and not being neurotic about working out and eating right. I started to enjoy life a little bit more."

Jennifer Lopez

Jennifer Lopez told Marie Claire, "I love to eat everything and you pretty much can a little piece of something fattening is not going to kill you."

Fergie

Fergie said to Marie Claire, "I have learned more and more to enjoy my body when I have a few extra pounds on, just being more voluptuous. I say, focus on the body part that you feel most comfortable about."

Khloe

Khloe Kardashian wrote on her Instagram, "We all have to start somewhere and doing something is better than nothing at all. Start small so you don't get discouraged and give up. Remember it is all about consistency."

Jennifer Hudson

Jennifer Hudson told Michigan Avenue, "For years, I felt like I could never have ice scream, but now I can eat ice cream occasionally!"

Kim Kardashian West

"For me, skinny is just a style of jeans...not a goal."

Adele

It's never been an issue for me - I don't want to go on a diet, I don't want to eat a Caesar salad with no dressing, why would I do that? I ain't got time for this, just be happy and don't be stupid."

Drew Barrymore

"I just think you should eat less of everything. A little bit less. I don't want to live a life where you can't have what you want; it just makes you want it more."

According to researchers at Oxford Brookes University in the UK, this method is superior to the BMI because measuring a person’s waist-to-height ratio takes their abdominal, or visceral, fat into account. For example, someone who isn’t overweight but carries a lot of fat around their middle would pass the BMI test, but not the string one.

This is important, because visceral fat has been linked to a higher risk of cardiovascular disease, type 2 diabetes and metabolic disturbances.

RELATED: Women don’t know what ‘healthy weight’ looks like

Almost 3000 people aged 16 and over had their health assessed for the study, which was presented at the European Congress on Obesity in the Czech Republic. Interestingly, the researchers found more than one third of the participants who were classified as “normal” under the BMI formula would have been flagged by the string technique.

http://cdn.theglow.com.au/app/uploads/2015/05/weight-health-indicator-01.jpg The number on the scales can only tell you so much.

“This study not only supports our previous findings on the superiority of waist to height over BMI as a primary screening method for morbidity and mortality risk, but also demonstrates the potentially severe implications of misclassification by BMI alone in screening for heart risk factors," study authors Dr Margaret Ashwell and Sigrid Gibson write.

“Checking that waist-to-height ratio is less than 0.5 could not be simpler: all that is needed is a piece of string, not even a tape measure.”

Will you be trying this one at home tonight?

How the rich and famous stay fit

Lena Dunham.

Girls star Lena Dunham says exercise is vital to her mental health.

Margot Robbie.

Miranda Kerr.

Miranda Kerr weights for nobody. (Instagram)

Rosie Huntington-Whiteley.

Anna Kendrick.

Gisele Bundchen.

Bar Rafaeli.

Kendall Jenner.

Lea Michele.

Karlie Kloss.

Paris Hilton

Julianne Hough.

Beyonce.