There's no hard/fast way to measure this. Do you do it on race? Or just foreigners? Or how they're treated in their country? Or the distribution of race in a country?
One international means of 'measuring' might be to look at the "Convention on the Elimination of All Forms of Racial Discrimination" - a document with 86 signatories and 175 parties.
Several of the parties have conditions on their signature, refusing to accept some parts. That doesn't necessarily make them racist though - for example, the ones refusing to ban hate speech do so (they claim) to protect freedom of speech laws.
Then you can look at who didn't sign or ratify the convention. As can be seen in the map above, there are a few countries - like North Korea, who didn't sign or ratify. Some might see that as a sign of xenophobia, some might just say they didn't agree with the wording.
Then of course, you have opinion on the most xenophobic/racist countries. There's an article on The Most Racist Countries in Europe. You also have a post on Answers.com claiming it's Saudia Arabia. Another claims Australia is one of the most racist countries.. Each has different ideas on 'most' depending on their Weltanschauung (view of the world).
Finally, a way to find out in depth about the types, levels and variety of racism around the world would be to read. Wikipedia has a page of Racism by country, broken down by continents, which you can use to find out about all the details of xenophobia - be it historic, cultural, religious, economic or demographic reasons