1 drop from eyedropper = .02 ml
1 teaspoon = 6ml
1 tablespoon = 20ml
1 ml = 1cc
1 teacup = 180ml
1 gm = 15 gr grains = 1000 mg
1 level teaspoon = 6gm +/-
1 level tablespoon = 20 gm +/-
1 teacup = 220 gm +/-
1 ppm = 1mg/litre -or- 1 mg/1000ml

Percent solutions are 1000mg/100cc. For example a 2% = 20mg/cc, 5% = 50mg/cc, 5.5% = 55mg/cc, etc...

Prepare a 1% solution of Malachite green (500 mg of powder in bottle). How many mL of sterile water will you use?
Answer: First convert 1% solution to mg/cc. A 1% solution is the same as 1000 milligrams in 100 cc or 10mg/cc.

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.