Printers using the CLI-221 & PGI-220 chips series include these Canon Pixma models:   

IP3600, IP4600, IP4700,
MP560, MP620, MP620B, MP640, MP980, MP990,
MX860, MX870

5 Cartridge Printers: IP3600, IP4600, IP4700, MP560, MP620, MP620B, MP640, MX860, MX870
 
6 Cartridge Printers: MP980, MP990  includes grey ink cart

CLI-221 Black is used in:
IP3600, IP4600, IP4700, MP560, MP620, MP620B, MP640, MP980, MP990, MX860, MX870

CLI-221 Cyan  is used in: 
IP3600, IP4600, IP4700, MP560, MP620, MP620B, MP640, MP980, MP990, MX860M MX870

CLI-221 Magenta is used in:
IP3600, IP4600, IP4700, MP560, MP620, MP620B, MP640, MP980, MP990, MX860, MX870

CLI-221 Yellow  is used in:
IP3600, IP4600, IP4700, MP560, MP620, MP620B, MP640, MP980, MP990, MX860, MX870

CLI-221 Gray is used in: 
MP980, MP990

If your model is not listed above, open your printer and look at the ink cartridges. They will be marked right on top with the chip series,

pgi-220 cartridges = 21 ml

cli-221 cartridges = 10.5 ml 

Be careful not to overfill, underfilling is always a better choice.