When I need to distinguish $f$ and $F$, I choose
- "small eff" vs. "big eff" / "capital eff". I find "uppercase/lowercase eff" to be a bit awkward; it doesn't run off the tongue as easily as the other options.
However, I might not distinguish them orally every single time. The flow of the lecture would determine when I would choose to emphasise the ...
There are two questions here.
The easier question is describing volume. There are two separate ways to measure volume. In metric terms, one standard measure would be liters and the other would be cubic meters. They are related in metric: one liter is 1000 cubic centimeters. Both of them (and their "American" counterparts) are extremely common and ...
Another example is that if you have lets say $30$ guests coming to your home, you want to buy cups for the tea or coffee or whatever but these cups come in dozens, i.e. there is only bags of $12$ cups, so how many bags you need?
They start for example $12+12=24$ not enough cups, $12+12+12=36$ now we have enough cups, so we need $3$ bags.
(Posting my comment as @ChrisCunningham suggests.)
How about: The number of days to their next birthday? This could involve: number of days remaining in this month, plus the number of days in the next month, the next, ..., until the number of days in their birthday month. Or, similarly: The number of days from now until Christmas: $13$ in November
plus $25$ ...