Best value Lexmark Ink Cartridges

The printer cartridge that you received with your Lexmark printer when you bought it is unlikely to be the most economical for you to purchase as a replacement.
The physical size of the cartridge does not vary, only the amount of ink contained inside.
Lexmark do not release details of how much ink each cartridge contains but do give details of the ISO yield measured in standard pages.

What is ISO?
ISO is a network of the national standards institutes of 156 countries, on the basis of one member per country, with a Central Secretariat in Geneva, Switzerland, that coordinates the system.
ISO is a non-governmental organization: its members are not delegations of national governments, as they are in the United Nations. Rather, ISO occupies a special position between the public and private sectors. Some of its member institutes are part of the governmental structure of their countries, or are mandated by their governments, while others represent national partnerships of private-sector industry associations.
Therefore, ISO is able to act as a bridging organization in which consensus can be reached on solutions that meet both the requirements of business and the broader needs of society, such as the needs of stakeholder groups like consumers and users.
These tests consist of printing a standard set of five pages, continuously, until the ink cartridge has reached the end of its life. This continuous method of testing is obviously less time consuming and expensive for the manufacturers to perform and whilst may allow an "apples to apples" comparison, bears little resemblance to real life situations.
The five pages chosen for example are unlikely to be replicated in actual day to day print situations and industry experts estimate that ink printer users only print a few pages at a time and that hours, if not days can pass before an other print job is requisitioned. This type of start/stop printing can dramatically reduce the page yield obtained from a cartridge. Inkjet printers use some ink to keep the printhead nozzles clear to allow the ink to flow smoothly and most printers perform a maintenance operation on start up which also depletes the volume of ink in the cartridge.
Some page tests are measured on page coverage of only 5% for black print, the standard letter test, and areas of solid black or areas of greyscale on the page will have an effect.

Unfortunately without knowing how much printer ink is in a cartridge, we are dependent on these figures and Lexmark do not make them available on packaging.
Searching for this information on their website is also not a straightforward task.

To confuse matters even further, Lexmark also produce two versions of many cartridges, a standard version and a Return Program version. The latter version is sold at a discount on the understanding that you return the cartridge to Lexmark when in runs out. They do this to ensure that these cartridges are not available to remanufacturers and thus decrease the competition for their highly priced original cartridges.

I do not believe by purchasing these cartridges that you are legally bound to return them to Lexmark and remanufacturers rely on people not doing so.
The best value cartridges for recent Lexmark printers carry the suffix XL and these in Return Program packs offer the greatest value.

Listed below are the part numbers of the cartridges that represent best value for current Lexmark printers.

Z series printers

Z845,Z1300,Z1310,Z1320,Z1410,Z1420
(18c0034) #34 High Yield Black Cartridge
(18c0035) #35 High Yield Tri-Color Cartridge

Z1520
(18y0144) #44XL High Yield Black Cartridge
(18y0143) #43XL High Yield Tri-Color Cartridge

Z2420
(18c2170) #36XL High Yield Black Cartridge
(18c2180) #37XL High Yield Tri-Colour Cartridge

X series printers

X2500,X2510,X2530,X3530,X3550,X4350,X4550,X5070,X5075,X5320,X5470,X5490,X5495,X7350

(18c0034) #34 High Yield Black Cartridge
(18c0035) #35 High Yield Tri-Color Cartridge

X4850,X4875,X6570,X6575,X7550,X7575,X9350,X9575

(18y0144) #44XL High Yield Black Cartridge
(18y0143) #43XL High Yield Tri-Color Cartridge

X3650,X4630,X4650

(18c2170) #36XL High Yield Black Cartridge
(18c2180) #37XL High Yield Tri-Colour Cartridge