From the tsp.gov web site:
You can contribute up to $17,500 in employee contributions to the TSP in 2014. The limit applies to the combined total of your tax-deferred traditional and Roth contributions. (This limit has not changed from 2013.)
If you are a member of the uniformed services, you can contribute a total of $52,000 in tax-deferred and tax-exempt money. (The 2013 limit is $51,000.)
Any participant who will be age 50 or over in 2014 can also contribute up to $5,500 in additional catch-up contributions, as long as regular contributions for the year are expected to reach the $17,500 limit. (This limit has not changed from 2013.) .