Sufficient pixels to print at 240 to 300 dpi is optimum to print photo images (speaking of photo images). Line art mode (black lines or text on white paper, NOT color mode) can use double that. More pixels really cannot help the printer, but much fewer pixels is detrimental to image quality. This is not difficult, but it is essential to know and keep track of.
This simple little calculation will show the image size needed for sufficient pixels for optimum photo printing.
The pixel dimensions do NOT need to be exact, but printing photos somewhere near this size ballpark (of 250 to 300 pixels per inch) is a very good thing. Here are some essential details of digital basics.
Cropping Aspect Ratio to fit the paper size is an important concern too.
And there is a larger dpi calculator that knows about scanning, printing, and enlargement.
Useful printing resolutions are shown below for common printing destinations, resolution at the scaled printing size on paper. Meaning if you need 4x5 inches at 300 dpi, then you need a 1200x1500 pixel image (a bit more or less dpi works OK too, just scale to print size). This printing dpi number is also the scan resolution if printing at 100% or original size, but enlargement of 1.5x needs scanning at 1.5x printing dpi.
For photos on photo-quality inkjet printers on Photo paper
240 to 360 dpi for color or grayscale, at printer's better quality setting. 300 dpi sometimes may be a little better than 240 dpi, but the difference is often hard to see.
For documents on inkjet good coated paper
Use a decent printer quality setting for the text, and photos around 240 to 300 dpi.
For inkjet printer using plain copy paper
150 dpi is often enough for images on plain copy paper. The ink soaks into the paper and spreads a little.
Coated inkjet paper is better, and photo paper is best.
For digital lab printing services
Drug stores, WalMart, Costco, Shutterfly, Snapfish, etc.
250 to 300 dpi, for up through 8x10 inch size. Many such machines are set to 250 dpi maximum, but 300 dpi still works fine (250 dpi is OK, these machines are continuous color, better quality than inkjets dithered color).
Inquire about crop size for wallet prints, 2.5x3.5 inches is conventional, but many shops are 2x3 inches.
Inquire about minimum pixel dimensions for poster size prints. But Minimum is a limit for refusal, optimal quality will be larger, probably all you can manage, because 300 dpi might be hard to provide for poster size.
For dye-sublimation printers
Near the dye-sub printer's dpi rating, which will be around 300 dpi
For laser printers, B&W or Color photos
300 dpi printer (54 lpi) - 100 dpi
600 dpi printer (85 lpi) - 150 dpi
1200 dpi printer (100 lpi) - 200 dpi
For commercial offset printing (photos for books and magazines)
Generally 300 dpi. Technically, image dpi between 1.5 and 2.0 (minimum and maximum) multiplied times the lpi specification for the screen process.
Most editors will routinely ask for 300 dpi images, which does Not mean your huge 24 megapixel image, but which only means at the final size to be printed (see the calculator above).
For printing photos in newspapers and newsprint
150 to 200 dpi (85 or 100 lpi) at final size.
Photos are No Go, because fax is line art mode, only black or white. Use email for photos.
For computer and TV video screens
Which is not all the same concept as printing. See the white "Video Screen" box here.
Line art for laser printers
300 dpi printer - 300 dpi
600 dpi printer - 600 dpi
1200 dpi printer - 1200 dpi
300 dpi line art is fine for casual purposes.
600 dpi is sharper for more critical line art work.
Line art for inkjet printers
600 dpi for best - but at least 300 dpi
Standard fax is 200 dpi line art
For commercial offset printing (books or magazines)
1200 dpi for commercial line art
For printing in newspapers
600 dpi is enough, cartoons for example
Inkjet paper quality makes all the difference when printing photos on a photo-quality printer. Paper Brightness rating is important for photos, with rating 94 being bright white, and 84 being drab in comparison. There are vaguely three main classes of paper for inkjets:
Plain copy paper is priced about $3 to $7 for a 500 sheet package, or about one cent per sheet. It is fine for laser printers and copy machines, but dye-based inkjet ink will absorb into plain paper and spread out (called dot-gain), and then high resolution is simply not possible. Some inkjets can use pigmented black ink instead of a dye-based black ink, which sticks to the surface of the paper, and helps give good results for black text on plain paper. But the colored photo quality ink is dye-based and thin (ink soaks in and spreads), and plain paper is quite poor for photo reproduction on an inkjet printer.
Coated inkjet paper has a smooth coating to hold the ink on the surface for better resolution (typically it’s the smooth/bright/white side). Price varies, more expensive, quality varies, there are many choices. The coating makes a difference for inkjets.
Glossy Photo paper looks like actual photographic paper and gives the best quality results for photo-quality inkjet photos. Glossy paper is the good stuff, and the photo-quality difference is like night and day on it. Matte photo paper works well too, which uses a different Paper Type setting.
If you are not getting the results you expect, be sure you are using good photo paper. All paper brands do not work quite the same on all printers, so judge results using the paper brand recommended by your printer. The paper is part of the printing system, the coating interacts with the ink, which is very important. Judge the color and quality after the ink dries.
Inkjet printer driver properties (some HP and Epson shown below) will have a place to specify the Paper Type. It is very important to specify the correct Paper Type actually used, because this setting controls the amount of ink used, to be appropriate for the paper surface (paper type).
For photo quality on the good paper, be sure to select a better ink dot dpi mode in your printer driver settings. This is NOT image dpi. It is a quality setting (often called Good, Better, and Best today) which is ink drops per inch. Be sure your image is large enough to have enough image pixels to print the image size you want, at the printed resolution you want.
There are a few things to check when you print.
Scale the image resolution to print the desired image size. Again, there are more details of essential digital basics HERE.
And in the inkjet printer driver (after Print Menu), set the:
Metric A4 size paper is about 8.2x11.7 inches and is closer to the shape of 5x7 inch prints or even 35 mm film than is 8.5x11 inch paper. You may like A4 size for full page photos.