The HP B9180 can display (or even print on the “Test page”) an estimate of how much ink is left in each of its eight ink cartridges. In 2007, after owning the printer for about a year, I measured how much ink it took to print each print in a series of nine A3 prints. The photos were provided by different photographers and were used for a small local exhibition. The prints were all in color and printed on borderless A3 HP Advanced Glossy photo paper.
Measured ink usage
This shows that, on average, roughly 0.75% of the total amount of ink (relative to a full set of cartridges) is used to print a borderless A3 photo. In other words, you could print in theory about 140 prints before consuming 8 cartridges (of 27 millilitres each). This doesn’t mean that you can print 140 photos starting from a fresh set of cartridges before the first cartridge runs out - some cartridges will drain much faster, while others need to be replaced much later. But again, we can use these average numbers to accurately calculate the cost of the ink used per print (see below).
The 3rd graph shows the amount of ink used for each of the prints. It is technically the “1st order derivative” of the previous graph: difference between 2 successive ink level measurements. This data highlights that there is quite some variation between individual prints. Print #6 was likely (I didn’t keep track) a relatively high-key portrait of a boy against a background of a light-colored tent.
My guess is that print #7 was a dark image of railway tracks.
Note that the relationship between images darkness and ink usage is actually more complex: a droplet of light grey or light cyan or light magenta ink counts (for a cost model) the same as a droplet of pitch black ink. Print colors that are lighter than the lightest inks will be created by decreasing the droplet density. And the exact way colors are mixed (e.g. to create green you need to mix cyan and yellow) further complicates the actual ink usage.
At a major, low-cost European Internet retailer, each ink cartridge costs roughly 30 €. Meaning that the ink for one borderless A3 print costs (on average) € 30 x 8 cartridges x 0.735% = € 1.76. So, to make this easier to remember, because ink costs vary and because the HP B9180 also uses a bit of ink for daily maintenance, let’s round this up to € 2 worth of ink per A3 print.
Photo paper cost
The corresponding special (“HP Advanced”) paper cost is € 25 for 20 sheets at the same Internet retailer. That amounts to € 1.25 per print for the paper (HP Advanced Glossy Photo Paper, “Q8697A”). So the total cost will be roughly € 3.50 per print if we add a bit of overhead for shipping (of both paper and ink – the actual shipping cost depend on how often you order and whether you order ink and paper from the same source).
Total costs of printer ownership
Say the printer costs € 350 (I have subtracted the price I would pay for the ink that comes with the printer, as we already accounted for that!). This “hardware cost” happens to correspond to 100 prints at € 3.5 each. So if you only print 100 prints before throwing away the HP B9180 printer, that would increase the real cost of an A3 print to € 7 per print (€ 2 for ink/paper, € 1.5 for paper, and another € 3.5 for the “hardware”). If you print 200 A3 prints within the lifetime of the printer, the cost per print drops to about € 5.25 (variable costs + 50%). If you print 400 A3 prints, the cost per print drops to € 4.4 (variable costs + 25%).
In other words, if you print (the equivalent of) hundreds of A3 prints, it is more important to try to get your “supplies” at the lowest possible price than to worry about the printer costs. Hopefully few people print less than 100 A3 prints during the lifetime of their printer – but people tend to be a bit irrational on these kind of things.
In practice, you may also use the same printer to print normal (non-photo) documents – I do that. These print pretty nicely and rapidly in either B/W or color. This makes the purchase of the printer even a bit more economical (as you would otherwise presumably need a simpler printer anyway, and may pay more for the ink on that one).
Cost compared to “having it printed”
The largest local serious photo shop charges about € 15 for an A3 (30 cm x 45 cm) print. This price partly reflects handling (e.g. grandma walks into shop with photo on a memory stick, CD or flash card) and occasional service if the customer is disappointed with the outcome (likely the image will be framed if someone takes the trouble of printing it A3 at a shop). Alternatively, if you submit the photo online and thus use a largely automated workflow, the price drops to about € 4 (www.hema.nl, a Dutch equivalent to Wall-Mart?).
Note that serious photography and fine-art printing services will use pigment inks (example of a high-end custom printing shop in the Netherlands). The cheapest external services presumably use dye-based ink, maybe use lower quality paper, and presumably worry less about calibration.