How many Jews live in the U.S.? That depends on how you define ‘Jewish.’

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Adolf Hitler wanted to eliminate the Jewish people, and his regime murdered 6 million in pursuit of that goal.

Thousands of Jews fled to the United States and Israel during and after the Holocaust, if they could manage to make it to these relative safe havens. Now, more than 80 percent of the world’s Jewish population lives in those two countries, and the American Jewish population has grown substantially in number since the end of World War II.

The Jewish People Policy Institute estimated that the global Jewish population was nearing pre-Holocaust numbers a couple of years ago, in part because of “changing patterns of Jewish identification.” But that finding was challenged because of the study’s broad definition of “Jewish.”

Like most things in Judaism, there’s disagreement. Here’s how two major scholars define Jewishness:

• Steven Cohen, a professor at the Hebrew Union College-Jewish Institute of Religion in Jerusalem, defines a Jew as “anybody who considers him or herself Jewish with some evidence of having Jewish familial ties or having affirmatively switched their identities by conversion or self-identification.” He says that being Jewish is not a religion but “a culture, an ancestry. Most practice Judaism, some don’t practice it at all and some practice other religions.”

• Hebrew University of Jerusalem’s Sergio DellaPergola defines the more narrow “core Jewish population” as those who are Jewish only or Jewish by identity, even if they are not religiously Jewish, as long as they practice no other religions. But he also calculates estimates for a more expansive group: those with Jewish parents, those partially Jewish, those with Jewish backgrounds and those who qualify under the “Law of Return” — any person born to a Jewish mother or converted to Judaism without another Jewish identity.

There’s even more to consider: Do you only count someone based on Jewish law if their mother is Jewish? Do you exclude those who practice Judaism and another religion? What about children in interfaith households? 

As a result, estimates of how many Jews live in the United States vary widely.

In 2013, the Pew Research Center released a study of the U.S. Jewish population and created a tool to estimate the size its size based on various definitions. 

For example, if you define Jews only by those who practice the religion, Pew counted 4.2 million adult Jewish Americans or 1.8 percent of the total U.S. adult population.

The estimated population would grow by 1.2 million if you include people of no religion who consider themselves Jewish in a cultural or secular way and have at least one Jewish parent. There are another 1.3 million children being raised at least partially Jewish and living in households with at least one Jewish adult. Totaling those groups, you reach 6.7 million Jews of all ages in the U.S. in 2013.

That’s more than the population lost in the Holocaust. 

But depending how you define the population and who is making the estimate, you could reach a different conclusion.

In 2016, the American Jewish Population Projectat Brandeis University estimated the U.S. Jewish population at 7.2 million. The American Jewish Year Book estimated 6.9 million. And DellaPergola at the Hebrew University of Jerusalem estimated the core U.S. Jewish population at a lower 5.7 million — but when he included all the other definitions of being Jewish his count of American Jews reached 12 million.

Based on those various calculations, it seems that the U.S. Jewish population has grown in absolute numbers since World War II, but it has not necessarily grown at the same rate as the country overall, according to Alan Cooperman, director of religion research at Pew.

So how does the current population compare with the American Jewish population soon after World War II? Twelve years after the end of the war, when many Jews had immigrated to the United States, the 1957 Current Population Survey (the only time the federal household count ever asked about religion) measured the U.S. Jewish population by religion at about 3.9 million people 14 and older. That’s less than the 4.2 million Jewish American adults by religion that Pew measured in 2013.

America provided a place where Jews could thrive and raise families in the years after World War II, even if it was not always welcoming to Jewish refugees. But it took quite some time — around 70 years — for the American Jewish population to match the number of Jews who were murdered in the Holocaust.