You can't directly convert milliliters (ml) to milligrams (mg) because they measure different things:

* Milliliters (ml) measure volume, which is the amount of space a substance occupies.

* Milligrams (mg) measure mass, which is the amount of matter in a substance.

To convert between volume and mass, you need to know the density of the substance. Density is the mass per unit volume.

Here's how you would do it:

1. Determine the density of the substance. For example, the density of water is 1 gram per milliliter (g/ml).

2. Convert milliliters to grams using the density.

* For water: 120 ml * 1 g/ml = 120 grams.

3. Convert grams to milligrams.

* 120 grams * 1000 mg/g = 120,000 milligrams.

Therefore, you need to know what substance you're dealing with to convert milliliters to milligrams.