FarO's self-answer suggests using the manufacturer's page counts. That's not a bad idea as a starting point, but let me add a few considerations.
- Those page counts are based on using all the ink in the cartridge. That would only happen if you turn it on, then print continuously until the ink runs out. If it is getting normal use, every time you turn it off, turn it on, pause more than a short time between jobs, etc., it uses a lot of ink to clean the nozzles. If you print intermittently, you may use more ink cleaning the print head than what goes onto the paper. Think of it as buying colored printhead cleaning fluid that also sometimes gets used to print. Also, some cartridges are detected as out of ink while there's still ink left. So you may get only a fraction of those page counts.
- Somewhere in their specs, Epson defines what a "page" is. It's typically defined in terms of size and coverage. You can compare what your own typical page consists of, and adjust. But unless your pages are radically different, other factors would probably make this exercise a waste of time.
- The page counts vary by color due to how much of that color is used in the mix on a typical page. The color mix in your printing may differ, which would affect the number of pages. Again, unless your printing is radically different, it probably won't be worth messing with this.
- Ink has a limited shelf life, even in the sealed cartridge (often on the order of two years). Don't buy more ink than you will go through in roughly a year. If replacement cartridges aren't readily available locally, do your best to estimate how much ink might be left, and get a replacement cartridge for each color to have on hand before that color runs out. Once you have actual usage statistics for each color, this will get much easier and more precise.
Which all leads to this. You need to start building your own history of ink usage by color vs. pages. If the usage data isn't accessible from the printer, keep track of paper usage (it doesn't need to be accurate to the page; the packages give sheet counts, so you can count packages and eyeball a fractional package).
Each time you replace a cartridge, the quality of your data will improve. Two or three cartridges of a given color will provide a pretty reliable estimate of actual usage. For the colors that last 10,000 pages or more, you might not go through enough cartridges to make it worth trying to estimate. But you could build your history of the shorter-lived cartridges and compare that to the manufacturer's page counts. Then use that to prorate the specs for the long-life cartridges. When you eventually need to replace one, compare that to the prorated estimate and adjust it for the next cycle.
You're starting with no data, so use the manufacturer's page counts as an initial basis. To ensure that you don't run out, tweak the numbers based on printing pattern and frequency (if it's very intermittent, maybe assume half the value). You can also check the page definition and adjust a little for that if yours is very different.
1Order a set ready, then keep your own records from now .... – Solar Mike – 2017-11-20T11:22:08.900
My question is about estimating past usage. Obviously I would do what you suggest, but there may be better solutions. – FarO – 2017-11-20T11:28:57.917
There is no way to estimate past usage. The printer cannot even tell you haw many pages it has printed, let alone how much ink it has used. This is true for most inkjets; high-end lasers may be different. – hdhondt – 2017-11-20T23:03:23.443