Information on the PVDM3 channel density is available here:
http://www.cisco.com/en/US/prod/collateral/modules/ps3115/data_sheet_c78-553971_ps10537_Products_Data_Sheet.html
With a proper CCO login, you can also access the Cisco DSP calculator here:
http://www.cisco.com/web/applicat/dsprecal/dsp_calc.html
HTH.
Regards,
Bill