"I'll give you the US CUs, but the differences are small. And I wasn't meaning that anyone can just mathematically convert units, but roughly compare them in everyday situations. For example, an 8oz bottle of water compared to a 1L bottle of pop. That was my error for not being specific."
Well I'm not sure which way you are going. But, no, the differences between U.S. Customary and Imperial are not small. In Orwell's novel, "Nineteen Eighty Four," that's why the old guy at the bar is complaining bitterly that the bartender will only draw him a liter or a half-liter, when he wants a pint. A half-liter is only 80% of an Imperial pint. (I couldn't figure that one out as a kid because I "knew" that a half-liter is almost identical to our "pint" and is actually just a bit bigger, so why would anyone complain about getting a half-liter instead of a pint?)
Talking to a U.S. speaker it depends entirely on whom you are talking to and what their experience is. In the special case of a liter, it just happens (for reasons I don't understand) that 1 liter is a very common soda bottle size, so many of us know that one liter is about a quart.
We have converted our athletic fields to Olympic standards but many of us are still very hazy on how long a kilometer is, or how fast 100 kph is. I think they are now using kilometers in the military, which they call "klicks."
Despite spending many years earning a degree in zoology and theoretically knowing SI, I never know how hot or cold the weather is, expressed in °C, without converting.
Until recently I wouldn't have known whether a man 180 cm. tall was very tall or very short. I know my weight in pounds but can't tell you even roughly in kilograms without actually doing some kind of calculation.
Most of us use and think in U.S. Customary most of the time.