You probably already know the difference between these two expressions. They sound simple and easy enough to use.
But at the moment of speaking, it's very common to confuse them and make a mistake.
First of all, “Short of” means to be low on something. Your supply of something is about 15%.
“Out of” means absolutely nothing. In short, 0%.
But if you put them inside a table, you will find that they’re not so easy to use. Especially when you add the Verb “run.”
Using the Verb “run” with “out of” and “short of” is very common. As you can see on the table above, the expressions are still clear:
Short of = 15% supply
Out of = 0% supply
But when you add the word “Run” to them, that’s when it gets confusing. “Run short of” and “Run out of” becomes very similar.
That’s why it’s practical (especially for non-native speakers) to practice them separately like this:
In other words, you can say:
Q: Why do you wanna go to the ATM?
A: I’m running short of cash. = around 20%
A: I’m short of cash. = around 15%
A: I’m running out of cash. = around 10%
A: I’ve run out of cash. = 0%
A: I’m out of cash. = 0%
Let’s take a look at another example:
Q: Why are you headed for the mall?
A: I’m running short of toilet paper. = around 20%
A: I’m short of toilet paper. = around 15%
A: I’m running out of toilet paper. = around 10%
A: I’ve run out of toilet paper. = 0%
A: I’m out of toilet paper. = 0%
As a final reminder, this is not a perfect rule and is only a guideline. For example, when talking about gas in the tank of your car or the battery of our various everyday devices (for example, cellphone, camera etc.), it's more common to use "out of" (but not "short of") and other expressions.
P.S. To learn more about this, please read "Battery English." Just click the link below: