Juli's answer is correct: 20 mEq is approximately 1,485 mg.

The conversion between mg and mEq is a bit tricky and requires some chemistry knowledge but I will note the calculations below.

"A milligram, abbreviated mg, is a metric unit of mass or weight defined as one thousandth of a gram. A milliequivalent is a measure of the quantity of ions in an electrolyte fluid. One milliequivalent is one thousandth of one mole of charges and is represented by the symbol mEq. The ions of different elements vary in mass, so it is necessary to know the atomic or molecular weight of the ions and their valence before a you calculate a conversion.

To convert milligrams to milliequivalents use the formula: mEq = (mg x valence) / atomic or molecular weight." [1]

Disclaimer: I am not a chemistry expert and am only tinkering with calculations based on a page which I am linking to at the bottom.

Potassium Chrloride (KCl) has a valence of 1 atom and a molar mass of 74.5513 g/mol.

1. 99 mg times a valence of 1 = 99

2. 99 divided by a 74.5513 molar mass ~ 1.33 mEq

3. 1.33 mEq goes into 20 mEq ~ 15 times

4. 15 times 99 mg is approximately 1,485 mg.

I don't think the dosage is meant to translate directly as they are taken in different forms. I wouldn't recommend taking a solid dose of Potassium Chloride to try and replace an electrolyte solution unless your doctor or pharmacist says it's okay. And I'd appreciate it if someone could verify the accuracy of my calculations and correct me if necessary.

[1] https://sciencing.com/how-to-calculate-solubility-from-ksp-13710440.html