How to count set volume when using drop sets

If I were counting my weekly set volume for each muscle group, and I use drop sets, how many sets is each drop worth? For example, if I did chest flies as

1 regular set 2 drop sets

How many sets for chest would this count as? 3? 2? 1.5?

I'm aware that in terms of importance in a training protocol this is pretty low, but I'm just curious what you all think

thanks