The question, as stated, cannot be answered sensibly. A cubic centimetre (cc) is a measure of volume, with dimensions [L3]. A milligram is a measure of mass, with dimensions [M]. The two measure different things and elementary dimensional analysis teaches that you cannot convert between measures with different dimensions such as these without additional information.
As a simple mental exercise consider a cc of air and of water. They will have very different masses.
20 cc
1/2 of a cc/ml
There is 20mg of NaCl in 200mg of a 10% salt solution. To convert mg to g, divide by 1000: 20mg = 0.02g of NaCl.
Simply multiply the mg's by the amount of pills. 20mg x 29 pills = 580mg in 29 pills.
In a 5mg/5mL solution, 20mL would contain 20mg of the active ingredient. To convert mg to cc, you need to know the density of the specific substance in question. This conversion cannot be accurately completed without the density information.
That is 5,000 cc
2,750 cc
250
20mg
20mg is approximately 0.0007055 ounces.
1 gallon = 3785.41 cc
473.176473 cc American568.26125 cc UK