All of our products are priced in GBP. 

If you are in a Euro based country, the amount you ultimately get charged is, therefore, down to the credit card company / bank you use for payment as it is them who performs the currency conversion. 

However, to get a very good indicator of the charge, you can normally just type the amount into Google and it will tell you the approximate exchange rate at your time of order (e.g. if you Google "Convert 21 GBP to EUR" it will give you an approximate amount based on exchange rates at that time).