How would you like to define race?
It does not make sense to try and define it biologically. Modern genetics can tell us a great deal about the source pools for your genetic ancestry using Y or mtDNA haplogroups for example, but how does that define “race” for a given individual or group? The best you could do with that kind of grouping is to say that prevalence for genetic variants within that group is different than the prevalence in a different group.
It is impossible to define it socially. Ask Shaun King, who feels his dad was a “light-skinned black,” but whose basic identification is based on how he feels he was raised.
In the US, it is simply a self-defined grouping, using (Federal) standards from the Office of Management and Budget. The standards were most recently revised in 1997 (I think) and in 2000 some OMB guidance was issued for implementing them. Not the first, and probably not the last, effort.
Two questions are used (one for race; one for ethnicity) and the sole determinant is the individual’s response.
Five race categories are created, and a separate one for Hispanic or Latino ethnicity.
From the guidelines:
*“The 1997 standards emphasize self-reporting or self-identification as the preferred method for collecting data on race and ethnicity. The standards do not establish criteria or qualifications (such as blood quantum levels) that are to be used in determining a particular individual’s racial or ethnic classification. They do not tell an individual who he or she is, or specify how an individual should classify himself or herself. Self-identification for race and Hispanic or Latino origin means that the responses are based on self-perception and therefore are subjective, but by definition, the responses are accurate.” *
Note that the purpose of the US Federal race standard is to drive data collection, and not to define race, per se. (Each individual essentially defines for himself which category he wants to associate with.)
Nothing wrong with coming up with your own definition of race, in which case the number of races would depend on whether you are a lumper or a splitter. But modern migration patterns would make the edges of your race categories pretty soft for any given individual.
My personal opinion is not of much value in GD, but “race” is kind of a meaningless term, and I’d be surprised if you got broad agreement on anything but discarding it except for casual shorthand.