Vitamin and mineral deficiencies, what is considered normal?

Hi, I’m taking iron and folic acid tablets as my levels were under what they should be. When I check various sites for minimum levels they all seem to vary so I don’t really know what to think of as normal levels.

On my blood test results it says normal folic acid should be 4.6 - 18.7. My serum iron level should be 7 - 26 and serum ferritin 15 - 300. 

Thank you for the information 😊