Experiment: I tested a viral TikTok theory that all McDonald's cups hold the same amount of liquid

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A viral TikTok from March appeared to show that three McDonald's drink cup sizes all had the same volume.
I set out to test whether or not that was true by measuring the amount of liquid in McDonald's sodas in small, medium, and large sizes.
I also did a pour test, transferring liquid from one cup to another to see if they all held the same amount of soda.
I found that McDonald's cups do not, in fact, have the same volume.
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Over half a year after it was originally posted, an incendiary TikTok from creator @mykah.mykah that appears to show three differently sized McDonald's cups holding the same amount of liquid went viral once again.

In a video captioned "they do be lying to us doe," @mykah.mykah — who appears to be wearing a McDonald's uniform — pours liquid from a small cup into a medium, and then into a large. The catch is that the liquid from the small drink cup appears to fully fill each cup, suggesting that each drink size actually holds the same volume of liquid.

@mykah.mykah

They do be lying to us doe, ##fyp ##fup ##foryoupage ##mcdonalds

♬ Wii store - Huge nonce

The video, originally posted on March 3, has amassed over 11 million views and approximately 1.6 million likes in the time that it's been live on TikTok. It's not quite clear why the video is receiving renewed attention over eight months since it was uploaded — the Daily Mirror published a story about the video on November 5, and the Daily Star on November 6. Since then, other outlets including Fox Business, USA Today, and The Daily Dot have covered the TikTok, helping to bring it into viral consciousness once again.

The video has one big red flag — @mykah.mykah doesn't show the empty bottom of the cups, meaning that there could potentially be liquid hiding out to boost the volume, a trick that Snopes reported has been used in similar viral videos

I set out to test the premise of the video for myself, making multiple McDonald's runs to confirm whether or not their cups indeed held the same amount of liquid.

First, I measured the volume of the soda contained within each cup

While I wasn't able to get the exact same cups that appear in @mykah.mykah's video, I ordered a small, medium, and large soda from two different McDonald's.

Before doing any pouring, I wanted a baseline of how much liquid was actually in each cup. While my measuring skills weren't perfect — I used a large mason jar and a Pyrex measuring cup — I was able to get a rough estimate of the liquid in each.

The small soda with ice contained just under 13 ounces of liquid (and partially melted ice) and the small soda without ice had about 14 ounces of liquid.

Left: the liquid contained in a small soda with ice; Right: The liquid contained in a small soda without ice. Palmer Haasch for Insider

The medium soda with ice contained approximately 18 ounces of liquid (and, once again, partially melted ice) and the medium soda without ice contained approximately 19 ounces of liquid.

Left: the liquid contained in a medium soda with ice; Right: The liquid contained in a medium soda without ice. Palmer Haasch for Insider

The large soda with ice contained slightly under 28 ounces of liquid (and — you guessed it — partially melted ice) and the large soda without ice contained approximately 27 ounces of liquid.

Left: the liquid contained in a large soda with ice; Right: The liquid contained in a large soda without ice. Palmer Haasch for Insider

These measurements weren't precise by any means, but they do give a ballpark estimate of the amount of liquid contained within each soft drink size at McDonald's, and make it clear that the capacity of a large is much bigger than the capacity of a small. Even before doing the pouring test, things weren't looking good for the theory that all of the cups had the same volume.

Pouring the liquid from cup to cup made it clear that the cups had very different volumes

I had to conduct the same test that @mykah.mykah did in the viral TikTok video in order to really prove that all McDonald's cups didn't have the same volume.

From that point, all I had to do was pour from cup to cup to see how much the soda contained within the small cup filled up the medium and large ones.

First, I poured from the small to the medium.

Pouring from a small McDonald's cup into a medium.

Then, I poured from the medium to the large.

Pouring from a medium McDonald's cup to a large.

Finally, I poured the liquid from the large back into the small.

Pouring from a large McDonald's cup into a small.

To really prove things, I poured the liquid from a full large cup into a small

Just to be completely sure, I poured all of the soda contained in a large cup into a small cup with a bowl beneath as insurance. It went just about as well as I expected.

Pouring a full McDonald's large cup into a small.

No, McDonald's cups don't all hold the same volume of liquid

Overall, my experiments clearly indicated that the large McDonald's cup does indeed hold more liquid than the small cup and that all three sizes have different capacities. That means that @mykah.mykah's original video from March is just another iteration of a well-done prank, albeit one with unclear implications — I was only charged one dollar for each differently-sized soda that I ordered at McDonald's.

Both McDonald's and @mykah.mykah did not immediately respond to Insider's request for comment.

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