The true cost of ink

Posted in: blog by Jack on 19 July 2007

The price tag on any given printer really tells only half the story. Many times the cheapest printer for sale isn’t necessarily the cheapest printer to own. And what’s the most affordable printer for you in particular? Depending on how many pages you print and how much it costs to print each page, a high-priced printer with expensive cartridges could be a lot cheaper to own in the long run than a less-expensive printer with low-cost cartridges. Coming up with that long-run cost for comparison isn’t always easy, but that is exactly what we did recently in PC Magazine Labs with some of the leading printers on the market. And the results were surprising.

Before you can calculate the real cost of a printer, you need to know the cost per page. To get it, you need two numbers for each cartridge: the yield (how many pages the cartridge can print) and the price. But until recently, there’s been no good way to find out the yield.

Printer manufacturers will tell you the yield they’ve found and, usually, the estimated cost per page. But printing different images, manipulating driver settings, or changing how you determine that a cartridge has reached the end of its life can all alter the yield you come up with. Without knowing if different manufacturers’ tests are comparable, you have to take the claims with a proverbial grain of salt.
What’s been sorely needed is a standard for yield testing. The good news is that there finally is one-for documents at least. (The standard for photos is still under construction.)

In theory, yield claims based on the ISO/IEC standard should be fully comparable, regardless of the manufacturer. But there’s always the possibility that different manufacturers have come up with different interpretations for how to run the tests, particularly with such a newly minted standard.

It’s easy to read more into the yield numbers determined by the ISO/IEC standard than they actually mean. The first thing you need to know is that they don’t represent a guaranteed number of pages you’ll get from every individual cartridge-not even if you’re printing only the set of pages defined by the standard. Basically, the stated yield is a statistical prediction that if you pick a cartridge at random and follow the procedures in the ISO/IEC standard, you’ll get at least that number of pages more than 90 percent of the time.

To calculate the yield for what the ISO/IEC standard calls a primary cartridge-black or tricolor, for example-you start with the individual results from a minimum of nine cartridges. More precisely, you need results from a minimum of three sets of three cartridges tested on each of three printers, to take variations among both individual printers and cartridges into account. (The standard defines a different approach for what it calls supplementary cartridges, such as light cyan or light magenta, but for our purposes that’s an unnecessary complication.)
You have to run the results through basic statistical formulas to determine what’s called the “90 percent lower confidence bound.” That number gets reported as the yield.

Knowing the cost per page for the printers you’re considering lets you compare running costs, but it doesn’t tell you which printer will be less expensive over its lifetime. For that, you have to calculate the total cost of printing, which means you have to make predictions about how much you’ll print and how long you’ll own the printer. If you know how much you print now, it shouldn’t be hard to make reasonably accurate predictions, based on how many monochrome pages and how many color pages you currently print per month.

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