The commission is proposing that charities with an annual income of more than £500,000 should give the number of full and part-time volunteers available to them in their annual returns.
"Volunteers represent a substantial resource, and are a potential risk, but no information is collected systematically about the scale of volunteering and its significance to individual charities," a spokeswoman for the commission said.
"We believe that by asking for a simple estimate from charities we'll be able to provide the public with basic information about levels of volunteering and it will also inform our understanding of the sector."
But charities have questioned whether this will be a sensible use of their time and money.
"It depends how accurate they want us to be," said a spokeswoman for the RNLI.
"We could always give an educated guess, but it wouldn't be a good use of our resources to count every volunteer."
Mark Restall, head of information at Volunteering England, questioned how helpful the exercise would be if figures were based on estimates and excluded small organisations.
"I would be a bit dubious about how useful it would be," he said.
"I think we'd probably be better off sticking to something with a known methodology such as the Cabinet Office's citizenship survey."
Charities can respond to the commission's consultation on the plans before March, at www.charitycommission.gov.uk.