You have been ordering McDonald’s fries wrong your whole life

Life is full of mysteries, such as how to reconcile quantum mechanics with the general theory of relativity, or how a person can attend a party and simultaneously be unaware that a party is taking place. These are, to quote Donald Rumsfeld, known unknowns. But there are other mysteries lurking in plain sight, strange phenomena relating to things that seemed solid, things we thought we could hold dear and true. Things like the relative value of McDonald’s fries.

“When ordering McDonald’s, my wife asked for medium fries rather than large ‘Because there’s not actually any more chips in them, it’s a con!’,” began Twitter user Everyone’s Favourite Jim (@JimmerUK).

Can this really be true? Could a conspiracy this far-reaching be taking place beneath our very noses? No. It is not. But something even stranger is true. 

To test the theory Jimmer first weighed the medium and large portions of fries, taking into account the weight of the box. The large contained 18g more. “Job done,” he thought. 

But then he realised that a large portion contained “116% of the fries but, at £2.29 vs £1.79, is 128% of the price”.

This got him thinking: “Surely, then, there is a point where it’s cheaper to buy more medium portions than large portions. Turns out, there is. And it’s not as many as you might think…”

It turns out if you buy five portions of medium fries you get more fries than buying four large portions, and you also save yourself 21p. The maths holds true for seven medium portions compared to six large portions, after which you will save money but get fewer fries, for mathematical reasons my smooth brain cannot fully comprehend. 

Jimmer has written up a comprehensive study of this phenomena on his blog, including a McDonald’s fries calculator that allows you to enter any number of large portions of fries and how many medium ones you should buy instead (it is cheaper to buy 195 portions of medium fries than it is to buy 167 large, for instance).

So there you have it – the mystery of the McDonald’s fries has been solved. For now.