Overal conversion rate:

Conversion Rate = Total Number of Sales / Number of Leads * 100

Conversion rate at any stage of a funnel:

Conversion Rate = Total Number of Leads Aquired / Number of Leads Approached * 100

Website conversion:

Conversion Rate = Total Number of Sales / Number of Unique Visitors * 100

Value of 1 lead:

Lead Value = Value of Sale / Number of Leads

Amount of leads needed to reach a financial goal:

Conversions Needed = Desired Revenue / Lead Value