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Dietitian reveals an easy trick for measuring portion sizes when you're dining out

Portion size calculation
YouTube/The University of Sydney
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Most of us struggle to measure how much food we're actually consuming when we're eating out. How much of this pizza constitutes a single portion size? How much pasta is actually in this bowl of spaghetti?

But now, a dietitian from the University of Sydney posted a YouTube video explaining the key to properly measuring portion sizes when we're on the go. The trick? Just use your hands.

"If you're trying to watch your weight and you're out to dinner, and you're presented with a bowl of food, there's no really good way to actually estimate how much you're eating, unless you're going to whip some scales out of our bag," dietitian Alice Gibson said in the video.

Gibson and a team of researchers sought to find a more objective way for people to measure how much they're eating when they're out and about.

The researchers got people to measure the width of their food using their fingers. They then used the geometric volume formula that most of us learned in math class when we were younger: volume = 1/2 (width times length times height).

Portion size calculation
YouTube/The University of Sydney

To demonstrate, Gibson brought out a piece of lasagna (which, for measurement purposes, is shaped like a box), a glass of wine (which they say is shaped like a cylinder) and a piece of watermelon (obviously, a wedge).

Gibson found that the lasagna was seven fingers by five fingers by four fingers, or V=1/2(7x5x4).

The researchers believe that the method should be incorporated into smartphone applications sometime in the future, where people can put in their finger width measurements, as well as their height and weight, and then let hte phone handle the calculations.

"And then you've got a more accurate way to estimate the portion size," Gibson said in the video.

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Lisa Ryan
Lisa Ryan is the executive editor of audience at Business Insider.Her team engages BI readers and helps make our journalism part of their daily routines. (And while you're here, make sure to sign up for BI's flagship daily newsletter — and download our app and sign up for notifications.) They also reach our off-platform audience across social and partnerships.Before this, Lisa was BI's head of newsletters, steering editorial strategy and overhauling our portfolio. Over the course of her career, she's also served as a senior writer at New York Magazine's The Cut, as well as a senior writer and editor of Katie Couric's daily newsletter. She previously covered law and policy at Law360, health at both BI and the Daily Mail, and hosted a culture podcast. She was selected as a UN Foundation press fellow twice, reporting from Uganda in 2016 and Rwanda in 2018.