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 to do the conversion:

1. Find the density of the substance. For example, the density of water is approximately 1 gram per milliliter (g/mL).

2. Convert the volume from mL to grams using the density. In the case of water, 118 mL would be equal to 118 grams.

3. Convert the mass from grams to milligrams. There are 1000 milligrams (mg) in 1 gram (g). So, 118 grams would be equal to 118,000 mg.

Therefore, you need to know the density of the substance to convert 118 mL to mg.