Most references available will give you the above guidelines to measure quantities.
However, you have to consider the fact that a "teaspoon" or "teacup" is relative, and you have to consider the substance you are measuring.
By way of an experiment, I took a teaspoon out of my cupboard and found the following results:
This level teaspoon gave me 3 grams of Potassium Permanganate, 2.3 grams of Virkon S but only 1.5 grams of Trichlorfon. The standard general guideline for a teaspoon is 5-6 grams.
One coffee cup gave me 490 grams of course salt, 340 grams of small high protein food, and 323 grams of medium sized pellets. A standard coffee jar will give you 700 grams of course salt.
Please bear in mind that when it comes to medication, the correct dosage is extremely important. Often, if you give to little, the parasites will not die and may become immune to the treatment. If you give to much, you may kill your fish.