Miles to km, yes. As another European, I know that because it's relevant to understand when they talk about speed limits, top speeds of cars, etc.
Pounds to kg... If it's written media, I just paste it to Google and get the conversion. If it's movies or shows, honestly I don't think I have found an instance while it actually matters at all. If a movie character says "Oh, no, I've gained 10 pounds in a month, I need to go on a diet" you know that they're sad because that's a non-negligible amount of weight, and knowing how much it exactly is doesn't affect understanding of the movie at all.
It's a similar situation to old novels talking about money... When you read a novel from 200 years ago talking about dollars, pounds or whatever, do you look at the historic inflation rate to check today's equivalence? You might, if you're a perfectionist, but the truth is that you can perfectly understand such novels without knowing that just by the context in which they mention money.
Pounds to kg... If it's written media, I just paste it to Google and get the conversion. If it's movies or shows, honestly I don't think I have found an instance while it actually matters at all. If a movie character says "Oh, no, I've gained 10 pounds in a month, I need to go on a diet" you know that they're sad because that's a non-negligible amount of weight, and knowing how much it exactly is doesn't affect understanding of the movie at all.
It's a similar situation to old novels talking about money... When you read a novel from 200 years ago talking about dollars, pounds or whatever, do you look at the historic inflation rate to check today's equivalence? You might, if you're a perfectionist, but the truth is that you can perfectly understand such novels without knowing that just by the context in which they mention money.