By the numbers: Same-sex marriage in the U.S.

The U.S. Supreme Court is set to begin hearing two days of arguments Tuesday in cases involving gay marriage. A look at the gay marriage issue by the numbers:

About 9 million: The number of Americans who are gay, lesbian, bisexual or transgender, according to a 2011 study by a scholar at the UCLA School of Law’s Williams Institute.

9 plus the Washington, D. C.: The number of states that issue marriage licenses to same-sex couples. The states are: Connecticut, Iowa, Maine, Maryland, Massachusetts, New Hampshire, New York, Vermont and Washington.

30: The number of states, including California, that ban same-sex marriage in their state constitutions. Ten states bar them under state laws. New Mexico law is silent on the issue.

Almost 9: The number of years gay couples have been marrying in Massachusetts, the first state to allow same-sex couples to wed. The Massachusetts Supreme Judicial Court ruled in November 2003 that it was unconstitutional to bar same-sex couples from marrying in the state. The court allowed weddings to start May 17, 2004.

49: The percentage of Americans who now favour allowing gays and lesbians to marry legally, according to a Pew Research Center poll conducted in mid-March. Forty-four per cent are opposed.

142: The number of days in 2008 that gay marriage was legal in California before voters banned it with Proposition 8.

About 18,000: The number of gay couples that married in California during the window when it was legal.

9: The number of justices on the Supreme Court. Six of the justices are married, all of them to people of the opposite sex. Justice Ruth Bader Ginsburg is a widow; Justice Sonia Sotomayor is divorced, and Justice Elena Kagan has never married.