http://www.mmo-champion.com/content/1971-Cataclysm-Currency-and-Honor-Ca...

For those who haven't heard yet, some of our existing currencies will converted to new currencies when Cata launches. Justice Points will become the equivalent of Emblems.

Your Justice Points total will be equal to (Emblems of Triumph + Emblems of Frost) * 2.75. The CAP for Justice Points is 4000. Ideally, we should all aim to have exactly 4000 Justice Points at launch, so that we can buy a nice item or two immediately.

Honor will work roughly the same way, also with a cap of 4000, just based on a different set of currencies and conversion rates.

The link above gives a nice breakdown of all the currencies affected, and a useful interface to plug in what you have now to calculate what you'll get in Cata.