How many mg equals 20ml?

The conversion of milligrams (mg) to milliliters (ml) depends on the density of the substance being measured, as mg measures mass while ml measures volume. For example, if the substance has a density of 1 mg/ml, then 20 ml would equal 20,000 mg. However, for substances with different densities, the conversion will vary. You would need to know the specific density to convert accurately.