Most medical insurance plans  reimburse based on Usual, Reasonable and Customary charges (UCR) for all covered expenses.

What is UCR  based reimbursement?
Usual Customary & Reasonable reimbursement  refer to an established maximum amount that an insurance company will reimburse for a particular medical service or procedure, covered under a health insurance policy.
UCR charges are generally based on prices that are typically billed by majority of providers, for each medical procedure or service, in a particular geographical area. The UCR can vary from one geographical area to another. The insurance companies use independent third party data, to determine the UCR for different services in different geographical areas.

for instance , if in a certain geographical area 95% of physician charge $100 for doctors consultation, than  a particular  insurance company, may establish the UCR  for that area as $100 for doctor’s visits and $100 is what  the maximum that the insurance may reimburse for doctors visit service in that particular area. UCR may differ from company to company.

Where can I see the established UCR for different areas?
There is no one certified source that provides this information publicly.
There are  private independent companies determine these charges based on extensive research. Insurance companies either collect this data or buy this data from these companies to establish their UCR.
You may call your insurance company to inquire or request for this information. You may also communicate with your service provider( doctor or hospital) and request their charges for a particular medical service.