Based on your provided information,

20mcg would be equivalent to 0.2ml, so 1/5th of a mL.

The strength of your compound is listed, so there is no conversion, just dosing based on your desired plan.

For example, 1mL has 100 mcg in it, which would be on the high side dosing for a novice. You'll want to start out with 0.5mL to test your reaction and adjust accordingly.