The statistic comes from the European Central Bank's study on Cash Use by Household in the Euro Area, published in November 2017.
The report presents estimations of the number and value of cash transactions in all 19 euro area countries in 2016, based on survey result as well as figures on main payments by demographic.
“The average card transaction value in the euro area was the lowest in Slovakia, Estonia and Latvia where it ranged from €16.05 to €14.33, indicating that consumers in these countries use cards for relatively low-value payments.” (p. 21)
“In 2016 euro area consumers carried on average €65 in their wallet. Germans carried on average the most (€103) in their pockets, followed by the Luxembourgers (€ 102) and the Austrians (€89) (see Chart 20). On the other hand, the Portuguese carried, on average, the least (€29), followed by the French (€32) and the Latvians (€41).” (p. 34)