The amount of ink in each cartridge, the cartridges are exactly the same and fit in your printer in the same way. The standard capacity HP 302 black cartridge contains 3.5ml of ink. The high capacity HP 302XL black contains 8.5ml of ink. The standard capacity HP 302 colour cartridge contains 4ml of ink, with the HP 302XL colour cartridge containing 8ml. The XL compatible ink contains 15ml black and 21ml colour.