for anything CPU-based (as opposed to TCAM-based), you will at best get an approximation of the maximum routes that can be held. It is largely determined by the amount of RAM. The 3825 has 1Gb of default RAM and can easily hold the entire BGP routing table (which currently consists of 500K + routes). Obviously with that many routes, your CPU can become a bottleneck factor as well.
I think could be find on the device specs, have you executed these commands:
show platform tcam + other arguments.
show platform hardware ip route summary
3800 - http://www.cisco.com/c/en/us/products/collateral/routers/3800-series-integrated-services-routers-isr/product_data_sheet0900aecd8016a8e8.html