The cost of informal caregiving for aging family members in the United States is estimated to be $522 billion a year, or about 15 percent larger than Virginia’s entire economy, a new study has found.

The RAND Corp. arrived at the estimate by tallying the hours friends and family devote to elder care and calculating the cost if that work were performed by unskilled workers earning the minimum wage. The cost would be higher — an estimated $642 billion a year — if skilled nursing care was used instead, the nonprofit organization said. By comparison, Virginia’s total GDP in 2013 was about $453 billion, according to the U.S. Commerce Department’s Bureau of Economic Analysis.

The study also found that three out of five of those family caregivers were also holding down jobs and often sacrificed income to balance their caregiving needs.

“These numbers are huge and help put the enormity of this largely silent and unseen workforce into perspective,” Amalavoyal V. Chari, a University of Sussex lecturer and the study’s lead author, said in a written statement.

Informal arrangements among family and friends are the primary method of elder care in the United States. Previous estimates have found that about one of every five adults is providing care to a relative or friend who is 50 years old or older.

RAND said the study, which was published online in the Health Services Research journal, took advantage of a new U.S. Bureau of Labor Statistics database, known as the 2011 and 2012 American Time Use Survey, to offer a more accurate assessment of the costs of informal caregiving. The BLS survey asks respondents to report the time they spent helping aging relatives with daily activities and their own employment status.

RAND researchers said previous attempts to pin down the cost suffered from a lack of detailed, nationally representative data.