The currency conversion fee is applied when the currency of the transaction is not the same as the currency of your card. For example, if you use your Airtm USD card to buy something online at a Venezuelan store that charges you in Bolívares, the charge will be made in VES and the Airtm USD will go through an automatic conversion process.
When carrying out operations with your Airtm card, the conversion fee will be dictated by MasterCard or Visa. You can use the Mastercard or Visa conversion calculator to calculate an estimate. If your currency is not listed, you can view an estimate at www.xe.com.