You can't directly convert mil-equivalents (mEq) to milligrams (mg) without knowing the molecular weight and valence of the substance.

Here's why:

* Mil-equivalents (mEq) measure the chemical combining power of an ion or molecule. It takes into account the number of electrical charges carried by the ion.

* Milligrams (mg) measure mass.

Conversion Formula:

To convert mEq to mg, you need this formula:

```

mg = (mEq * molecular weight) / valence

```

Example:

Let's say you want to convert 10 mEq of potassium chloride (KCl) to milligrams.

* Molecular weight of KCl: 74.55 g/mol

* Valence of K+: 1

```

mg = (10 mEq * 74.55 g/mol) / 1

mg = 745.5 mg

```

Therefore, 10 mEq of potassium chloride is equal to 745.5 mg.

Remember:

* You need to know the specific substance to determine its molecular weight and valence.

* This conversion is only applicable for electrolytes.

If you need help converting a specific substance, please provide its name and any relevant information.