How many drachmas are in a mina?

Could you please clarify for me how many drachmas constitute a mina? I'm trying to get a better understanding of ancient Greek coinage and its conversion rates. Is there a specific ratio or is it variable depending on historical periods or regions? Your insight into this matter would be greatly appreciated. I'm also curious to know if there are any other important considerations I should be aware of when dealing with these currency conversions. Thank you for your assistance in this matter.