The U.S. census race definitions says a "black" is a person having origins in any of the black (sub-Saharan) racial groups of Africa. It includes people who indicate their race as "Black, African Am., or Negro" or who provide written entries such as African American, Afro-American, Kenyan, Nigerian, or Haitian. The Census Bureau notes that these classifications are socio-political constructs and should not be interpreted as scientific or anthropological. Most African Americans also have European ancestry in varying amounts; a lesser proportion have some Native American ancestry. For instance, genetic studies of African Americans show an ancestry that is on average 17–18% European.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): How does the U.S. census define "black" Americans?
having origins in any of the black (sub-Saharan) racial groups of Africa