The statistic comes from the 2018 report Trends and Developments in the Use of Euro Cash Over the Past Ten Years, published as part of the ECB Economic Bulletin, Issue 6/2018.
Euro banknotes are used daily by 340 million European citizens in private and professional transactions. Across the EU in 2016, an average of 79% of all point-of-sale transactions were carried out using cash.
The value of euro banknotes in circulation grew continuously during the period from January 2008 to December 2017, with an average annual growth rate of 6.1%. At the end of 2017, the total value of euro banknotes in circulation was €1,171 billion, with an annual growth rate of 4.0%.
The €50 is by far the most circulated banknote. The €500 was the denomination with the highest share of banknotes in circulation in terms of value until April 2012, after which point the €50 became the most important denomination.