Charities calculation

1.5 million US nonprofits (source; Charity Navigator gives the same number). Of those, around 1.1 million are public charities (source).

AmazonSmile allows a choice among “almost one million eligible 501(c)(3) public charitable organizations”.

61 charities in GW spreadsheet which is “a list of charities focused on evidence-backed, potentially cost-effective programs whether or not we have investigated them” (source). This list includes top charities.

From GiveWell’s old charities page (as of August 16, 2016):

As of November 2015, Charity Navigator has rated 5000 charities based in the US (source).