Football Fields

Here's a thought: I'm always seeing videos or articles that try and give you a sense of how big (or small) things are. For example, if a hydrogen atom was the size of a football field, the nucleus would the size of a grain of salt.
That's all well and good (except it's pointless to try and comprehend that sort of scale. But that's for another post).
The thing is, comparisons using the size of a football field are really common in these things. Pretty much everything is measured relative to a football field when a science is thrown at the public. My - perhaps trivial - question is: what kind of football field? They use the same comparisons in the USA and the UK, only here we mean football fields, and in America they mean American football fields.
It's not important, it's just something to think about.