If you've made a "backup" for your game, run it through NDS Header Tool and it'll give you tons of info on it.
E.g. Mario Kart DS (E):
Internal Name: MARIOKARTDS
ID: NTR-AMCP-EUR
Card Size: 256Mbit (33554432 bytes) (08h)
CRC32: 6E4CEDA1
plus some other stuff. It's in the GBATemp download center.