Ink levels and page counts

Question: So how does an inkjet printer know exactly how much ink is left inside a cartridge?

Answer: It doesn’t. It approximates.

Courtesy of Hewlett-Packard)

Courtesy of Hewlett-Packard)

Printer manufacturers install firmware (so called because it’s the software that controls a piece of hardward) into every printer they sell. The firmware contains drivers and the interface between the user and their printer. It’s what determines the ink level in the cartridge.

But how does it do that? There’s no float or other mechanical means of measuring the ink remaining in a cartridge. It is able to accomplish this by using an algorithm and counting pages.

If you took all the content on an 8½x11 printed page and condensed it into a solid block it would cover 5% of the page.

pagecoverageThe image to the left illustrates 5% page coverage. As you can see, it’s a fairly average amount of text for a letter.

So every time your printer uses enough ink to cover 5% of a page an internal counter ticks off one page. When the counter reaches page number 150, 495 or however many pages the manufacturer has rated the cartridge to produce you’ll be notified your cartridge is out of ink. It may or may not really be out of ink, but your printer thinks it is.

Your printer may not allow you to continue printing until you replace the cartridge, even though it may still contain a small volume of ink. This is something else that’s coded into the firmware.

Not all cartridges are created (or filled) equally and as a result yield different page counts.

For example, the HP 02 series of color ink cartridges come in three ink volumes, but only two are obvious. There’s a physical difference in the shape of the HP 02 cyan and the HP 02XL cyan. However, if you buy an HP 02 cartridge bundled with photo paper you’ll be getting a cartridge identical in appearance with the standard 02 cartridge but with less ink inside. Staples includes a disclaimer, “Value ink cartridges are smaller in size than single cartridges” on the description page of these underfilled cartridges. They aren’t truly “smaller in size”, but rather smaller in ink volume. Some HP cartridges will have a number on them similar to “CC604FN” or “C8773WN”. “FN” generally indicates a low yield HP ink cartridge while “WN” indicates a standard or high yield cartridge.

When we refill these cartridges we use the quantity of ink required for the high yield or “WN” cartridge. When you purchase these cartridges, whether new or refilled, it pays to be sure what ink level you’re getting and how many pages you should expect from them.

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