The National Fraud Authority will invite 10,000 charities to take part in a survey that will attempt to discover how much fraud takes place in the sector.
The NFA produced estimates last year suggesting that £32.2m was lost to fraud in the sector, based on data available at the time, but it believes that figure is too low.
Catherine Hayes, research and analysis manager at the NFA, said: "The NFA is conducting this survey among 10,000 charities of all sizes and across many sectors to allow us to get a better picture of how big an issue fraud is for charities.
"The more we understand this problem, the more we can do to help charities protect themselves better."
The results of the survey will feed into the second Annual Fraud Indicator, a measure of all fraud in UK business, which will be published in early 2011.