In the world of three-letter acronyms, use of the ISO images-per-minute (ipm) standard to rate printer speed has reached critical mass, so it's time to convert.Having seen enough people using it to treat it as common currency, it's time to talk about printer speeds in terms of the two-year-old ISO/IEC 24734 spec, which mandates how to measure printer throughput. Whereas each vendor formerly derived their own printer speeds each in their own way, the ISO standard offers a suite of test documents and a methodology for measuring throughput.
Basically, the ISO provides three sets of test documents, each with four pages. One set is Microsoft Word files, one set is Microsoft Excel files, and the third is four PDF files. Each file has one page. You can see them here.
As you can see, they are not heavily laden with graphics, but are more representative of what people do in administrative offices rather than in advertising agencies. There are some corporate logos and one photo that's an eighth of the page. The rest of the artwork is graphs and diagrams.
The methodology is rather complicated, and the resulting tests are supposed to be repeated until the results are consistent within plus or minus 5 percent. The term to know is ESAT (Estimated Saturated Throughput) which is the print rate after the first test set of files has been printed (and initial file transmission to the printer is complete.)
The upshot is that people seem to be using images per minute (ipm) to refer to ISO test results, although some refer to ISO ppm. Standing by itself, ppm seems to refer to legacy ratings, based on the vendor's methods rather than the ISO test.
The other upshot is that sources agree that the ISO ipm ratings can be expected to be lower than legacy non-ISO ppm ratings. In fact, Canon has a video of one of its printers, rated at 8.1 ipm, going head-to-head with the printer of an unnamed competitor rated at 38 ppm. The Canon appeared to be about twice as fast.
There does not appear to be a standard ipm/ppm ratio, probably because one is not possible.
Anyway, there are enough apples v. oranges comparisons in this arena. If you see a printer throughput estimate without any explanation of how it was derived, ask for the derivation.