Contact your bank or credit card company and ask what the fee is for exchanging foreign currency into U.S. dollars. Record that percentage.
Log onto the Internet and find the current exchange rate. A quick search will give you the current rate.
Using a calculator, multiply the amount of your Euros by the exchange rate. For example, if you wish to exchange 100 Euros, multiply 100 by the current exchange rate; at the time of this writing, one Euro is equal to 1.4280 U.S. dollars. Therefore, you would receive: 100 x 1.4284 = $142.84.
When exchanging Euros for U.S. dollars, subtract roughly 1%-3% from the total, this amount representing fees to the bank and/or credit card company for performing the exchange.