[General] and hour or per hour?

[JarekSteliga]

Can I use "an hour" in "20 miles an hour" to indicate speed? Or is it always "per" unit of time to express speed?

Another thing - wages/salary. I understand both "per" and "an" are acceptable here i.e. we can say, "She is earning 2 pounds per/an hour". Am I right?

 

[CarloSsS]

NOT A TEACHER

As far as I know, "per" and "a" used like that are interchangeable and therefore the answer is yes to both of your questions. For what it's worth, "per" sounds a little more formal to me.

 

[SoothingDave]

Yes, you can use either "per" or "an" in these uses. "An" is easier to say in phrases like "miles an hour."

 

[riquecohen]

Speed limits are sometimes posted with the number followed by MPH (miles per hour.)

 

[CarloSsS]

Speed limits are sometimes posted with the number followed by MPH (miles per hour.)

Do you mean speed limits on traffic signs?

 

[emsr2d2]

Do you mean speed limits on traffic signs?

I think that is what he meant but, in the UK, I don't think I've ever seen an actual speed limit sign on any road which says MPH after the number.

 

[SoothingDave]

You see it on yellow "caution" type signs, but not normally on white speed limit signs.

 

[5jj]

Here's the British version/.

 

[emsr2d2]

Here's my favourite (!)