Shopping can be extremely difficult these days 鈥 we all know a certain size at one store doesn鈥檛 always mean you can wear the same size at another. This is thanks to a retail phenomenon called vanity sizing. Rather than going by a uniform sizing standard across the board, retailers set their own sizes based on their customer shopping base.

PALM SPRINGS, CA - 1954: Actress Marilyn Monroe poses for a portrait laying on the grass in 1954 in Palm Springs, California. (Photo by Baron/Getty Images)

Once upon a time, women鈥檚 sizes ranged from size eight to size 42. According to the Daily Mail, the British Standards Institution recently released a guideline showing that Marilyn Monroe 鈥 long considered to be a curvy, body-positive role model who was famously a size eight back in the day 鈥 would actually fit into something more like a size four today at one of your favorite stores.

LOS ANGELES, CA - MAY 07: Kim Kardashian West attends the book signing for "Selfish" at Barnes & Noble bookstore at The Grove on May 7, 2015 in Los Angeles, California. (Photo by Jason Merritt/Getty Images)

Meanwhile, the same article states that Kim Kardashian, who wears size 10 in today鈥檚 sizes, would have worn a size 14 in the 鈥70s. In other words, vanity sizing really throws things off.

According to the Washington Post, sizing guidelines were once maintained by the National Bureau of Standards but were abandoned because ultimately 鈥渨omen鈥檚 bodies defied standardization.鈥 While that is absolutely true and something to be proud of, we can鈥檛 deny that vanity sizing can make shopping extremely difficult and frustrating for consumers.

At the end of the day, it鈥檚 always great when something fits true to size, whatever that size might be.

What do you think of these clothing size guidelines? Tell us in the comments below!

(h/t Daily Mail, photos via Baron/Stringer + Jason Merritt/Getty)