Credit: Instagram/WODthefork

A body-positive Instagrammer’s post about why clothing sizes shouldn’t be trusted is going viral, and for the very best reason.

Instagrammer and health blogger Katy (@WODTheFork) posted two side-by-side photos of herself in an Express dressing room as she attempted to try on leggings. Though she’d selected two pairs of leggings in the same cut and size, they each had a drastically different fit on her body.

While one pair of leggings fit her easily (and were even a little too big), the second pair of leggings were too tight to even fit up over her thighs.

Katy’s post brings to light the sad truth about American clothing sizes, which is that they are completely arbitrary and unstandardized, even when they come in the same style from the same store.

In fact, The Washington Post published a chart on women’s clothing sizes that essentially proves how unreliable the sizing system really is. In 1958, a woman who wears today’s size eight would be wearing a size 16. Back then, a size-eight woman weighed 98 pounds and wore a size smaller than today’s 00. Sometimes, a size will be lowered to be more appealing to the consumer. According to Lynn Boorady, “vanity sizing specifically is when the size on the label is lowered artificially in order to attempt to get someone to buy the garment.”

In other words, vanity sizes mean nothing. The value of our bodies — and very selves — is not something that can be quantified by a number.

When you’re a woman growing up in a world that tells you otherwise, this can be a very difficult lesson to learn. Luckily, we have women like Katy helping to reinforce the positive message that clothes are just clothes. That number on the tag holds no power over us.