The US single and multi-family office sector oversees a total of $1 trillion of assets and the minimum amount of money that a family must typically have to set up to create an office has more than doubled over the past two years to $250 million, according to a new study.

There are between 500 and 1,000 single family offices in the

US, according to the report by Celent, the US-based consultancy and research firm, underscoring how it remains difficult to obtain exact figures on this traditionally discreet part of the wealth management industry. The report says there are between 2,500 and 3,000 multi-family offices in the US.

Celent also estimates that, in the

US, single family offices have about $300 billion of assets while multi-family offices manage and advise on an additional $750 billion of assets.

Family offices represent over 20 per cent of the total $2.4 trillion held by retail investment advisor clients in the

US, explaining the strong interest the space has received in the last few years, Celent says.

The report is entitled US Family Offices: Best Practices in Providing Financial Services to

America's Most Privileged Households.

Estimates from two years ago were that at least $100 million in assets need to be placed into the single family office to make it worthwhile to operate. That number has risen closer to $250 million today. According to studies, the typical single family office costs about $3 million a year to operate and employs approximately 10 full-time staff.

While the proportion of households with family offices may be small, the proportion of wealth they control is more substantial, estimated at over $1 trillion (or 20 per cent of all ultra-high net worth households' assets).

It is estimated that there are 1,000 single family offices in operation around the world catering to families with at least $100 million in assets. More than half of these single family offices are managing family wealth of more than $1 billion.

“Celent expects the number of wealthy families seeking the benefits and full suite of services of multi-family offices to increase. However, we also expect to see competition increase in this space as non-traditional providers such as wirehouses, trust companies, private banks, and other registered investment advisors seek to crowd into the space,” the report says.