Religion in the United States is worth $1.2tn a year, making it equivalent to the 15th largest national economy in the world, according to a study.

The faith economy has a higher value than the combined revenues of the top 10 technology companies in the US, including Apple, Amazon and Google, says the analysis from Georgetown University in Washington DC.

Co-author Brian Grim said it was a conservative estimate. More than 344,000 congregations across the US collectively employ hundreds of thousands of staff and buy billions of dollars worth of goods and services.

More than 150 million Americans, almost half the population, are members of faith congregations, according to the report. Although numbers are declining, the sums spent by religious organisations on social programmes have tripled in the past 15 years, to $9bn.