Dots Per Inch
Let’s look at the basics. Printers print by putting ink or toner onto paper. Inkjets have nozzles that spray tiny drops of ink, while laser printers melt dots of toner against the paper. The more dots you can squeeze into a square inch, the sharper the resulting image will be. So, the most common printer spec is dots per inch, or dpi. A common spec is 1,200 dpi, though some inkjets have a higher vertical resolution (they can put more dots top to bottom than left to right), so you might also see something like 720x360 dpi.
Printers can put dots of different sizes, intensities, and even shapes, onto the page, which can change the way the finished product looks. Many printers use “optimized dpi,” meaning their printheads optimize the placement of ink drops to improve the quality of prints. If you see a printer that has a 9,600 dpi, it’s layering dots by passing the same part of page multiple times and putting several dots of different colors in one place. The final result will look rich, but this technique uses a lot of ink and time.
Print at the Resolution You Need
More is not necessarily better. For the majority of daily uses you’d be wasting ink to print everything in the highest possible resolution. When I print out shopping lists, I set my printer to “draft” quality so the document comes out fast. It doesn’t look perfect, but who cares? As long as I can read it when I’m in the supermarket, it’s good enough.
What’s Good Enough?
For a letter or business document (even one with graphics), 300 dpi is going to look fine. If it’s a handout for the board of directors, 600 dpi will look great. For the average photographer, 1,200 dpi is excellent (only pros would need to print something at twice that). All of those specs are well within the means of every decent printer out there. And once you get above 1,200 dpi, it’s going to be nearly impossible to see any difference in whatever you’ve printed.
Ink Makes a Difference
Resolution is more than just dpi, however. The kind of ink used can trump the dpi numbers. Laser printers will make text look sharp because they use toner which doesn’t bleed into the paper like ink does, so if your main purpose in buying a printer is for printing black-and-white documents, a monochrome laser printer will give a page of text that looks crisper than a high-resolution inkjet printer.
Use the Right Paper
Papers are made to optimize the differences between printers and so help create great images no matter what dpi your printer is capable of. Plain copy paper will work well for laser printers because nothing is getting absorbed. But inkjet inks are water-based and so they get absorbed into paper fiber. That’s why there are specific papers made for inkjet printers (and why printing a photo on plain paper is going to give you a limp, wet picture). If you’re just printing an e-mail, use cheap copy paper; but if you’re developing a brochure or flyer, it's worth investing in the right paper.