As of the 1st of January 2014, 18 of the European Union's 28 countries use the euro.
19 European Union countries use the Euro as their countries, plus 2 other countries in Europe.
10 countries in the EU currently don't use the Euro.
If you mean how many countries in the EU use the EU currency, the Euro, the answer is 17.
EU, I think means euro, like the currency of Europe €
the euro
Denmark did not leave the EU. It is still a member. It does not use the Euro, but that does not mean it is not in the EU. Some other EU countries do not use the Euro. Only 19 of the 28 member countries use it.
Montenegro and Kosovo are countries that are not in the EU but use the Euro (Kosovo also uses the Serbian Dinar)
The EU is just the European Union. Any countries of Europe can apply to receive EU membership if they qualify. The EU (or Euro) zone is the collection of member countries which share the currency the Euro. The Euro is now compulsory for all EU members, except the UK and Denmark which have opted out but may join in the future.
Euro is the official currency of the European Union. However, some countries inside the EU, decided to keep their traditionnal money (UK sill use the Pound). The Euro zone is the group of countries that had adopted the Euro (€) as their currency. On the 27 countries in the EU, 15 countries belong to the zone Euro. The other countries have either refused (UK, Sweden, Denmark....) adopting the Euro or are waiting for their Economies to be fit with the legal economics demandings defined by the EU.
The euro is the unit of currency used by many EU member nations. It replaced each country's own currency, and as such the euro doesn't need to be exchanged when travelling between countries. The German mark, French franc, Austrian schilling, Irish pound, and Italian lire were all replaced.
Euro, as in 11 other EU-countries. However, not all the EU-coutries have euros, like the UK and Sweden.
The currency is called the Euro, not the Euro Dollar. Not all countries in the European Union use the Euro. There are 28 countries that are members of the European Union. 18 use the Euro. 10 use their own currencies.
If EU represent EURO currency, the advantage is that in Europe many countries have adopted EU for transactions. Tourists and travellors need not exchange currency.
The Euro is the official currency of the European Union, although not all Eu countries use it yet. Its lower denomination is the cent, of which there are 100 to 1 Euro.