Do You Know the Secret Feature of the Iconic Red Solo Cup?

If you’re attending a backyard barbecue, pool party, or any kind of group gathering this holiday weekend, chances are someone’s going to offer you a beverage in a red Solo cup (or its off-brand ilk). Long before it was immortalized in song, the disposable, recyclable, and brightly colored plastic cup has been a de facto accompaniment to good times in the good old U.S. of A.

Here’s why it’s so iconic — including a secret that you may not know.

Although the Solo Cup Company has been making paper cups since 1936, it wasn’t until the 1970s — the decade of Animal House and Dazed and Confused — that the plastic version was first released and immediately adored by collegians, campers, and backyard burger-flippers alike.

Officially called the Party Cup, it was originally introduced in four sizes and four colors, but it’s the red 18-ounce version that’s risen to iconic status. The company is tight-lipped about its sales figures, but recent reports attest that red outsells blue by a vast margin (more than half of Solo’s overall party cup sales) — and most speculate that the gender-neutral hue is a big part of its runaway appeal.

And here’s something you might not know about the party staple: it’s not just a place to pour your drink, it’s a place to measure your drink too!

Yep, the lines on the classic cup design aren’t just for aesthetics or grippiness — in an act of kismet, they correspond to common fluid-ounce measurements. Starting from the bottom up, they mark one ounce (a perfect shot of bourbon for your Boulevardier or gin for your Negroni); five ounces (a standard wine pour); 12 ounces (a typical can of soda or beer); 16 ounces (aka a pint); and the final 18-ounce mark for any overflow from ice.

These seem too coincidental to not be by design, but Dart Container Corporation, Solo Cup’s present owner, responded to a recent Gizmodo piece and disavowed any intentional correlation between the design and these standard measurements.

It does seem awfully coincidental however; perhaps the corporate line is to avoid any public encouragement of alcohol consumption? Conspiracy theorists, feel free to theorize. In the meantime, take a look at the company’s “official” take on what the lines on the cups actually mean (click image to embiggen).

Now that Solo changed its design to the square-bottomed cups, the lines no longer exist on the brand-name version, but they’re still around on the generic brand, which retains the original 1970s-era design. (Nostalgia? Or a preference for functionality?)

So if you’re ever in a pinch and can’t find your trusty Pyrex measuring cup while you’re cooking, you can always grab a cup from your party stash and save the day.