It isn't necessary to convert to grams. Let's say the recipe is:
60% secret ingredient.
The recipe always adds up to 100%.
So, to make a 100 gram recipe, you would just do
10 grams powder
30 grams liquid
60 grams secret ingredient.
If 100 grams is too large a batch for you, and you only want to make a 25 gram batch. Well, 25 is 1/4th of 100 so you would mix:
2.5 grams powder
7.5 grams liquid
15 grams secret ingredient