The Disasters Emergency Committee estimates that it spent £1.5m on Google advertising during its emergency appeal for people affected by Typhoon Haiyan in the Philippines, which raised more than £90m.
It is understood that DEC members spent a similar amount on the more recent appeal for the earthquake in Nepal, but a DEC spokesman declined to give details on the grounds that it might give the charity's competitors an advantage.
The £1.5m spent on the Haiyan appeal was the cumulative spending of all of the 13 DEC member agencies on Google's paid advertising product, Google AdWords. Most of the charges, calculated on a per-click basis, were made during the three-week peak of the appeal in November 2013.
The DEC spokesman acknowledged the spending figures were significant and said the charity had approached Google about reducing its AdWords costs.
A spokeswoman for Google said it had given more than £20m to UK charities through programmes such as Google for Nonprofits.