The dimension in pixels (Image Size) is the important detail for using any image. Around 300 pixels per inch is the optimum and standard proper printing goal for color photographs. 200 dpi can sometimes be marginally acceptable printing quality, but more than 300 dpi is not of use to printers (for color photos), because our printers are not designed to do more for color work and our eyes cannot see greater detail (color work). Many local 1-hour photo lab digital machines are usually set to print at 250 pixels per inch, but it won't hurt to always provide pixels to print 300 dpi. 250 to 300 dpi is a reasonable and optimum printing resolution for color photos. However Line Art mode (two colors, black ink on white paper, like text or cartoon lines) is normally better scanned and printed at 600 dpi.

FWIW, I'm old school, and I learned the term for printing resolution was "dpi", so that's second nature to me. Dpi has simply always been the name of it. Some do call it ppi now, pixels per inch, which is what it is, same thing. Ink jet printers do have their own other thing about ink drops per inch which they also named dpi, but which is about the quality of dithering colors (to color each pixel, to be one of 100s of thousands of different colors created using only four colors of ink), but that is Not about image resolution. But here, we're speaking of images, about printing resolution of image pixels, which ink jets also have to do.

Things to be sure you know about printing

The dpi calculator is below, but first, some things you need to know. There are two situations when printing images, depending on if using one hour print shops or home printing.

• The photo printing shops where we order prints will offer a paper size, and will fill that paper with your image. They will ignore your dpi number already in the image file, and will recompute their own necessary "pixels per inch" value, to scale your image to their paper size. If you order 8x10 inches, you will get 8x10 print size, but you may not get your entire image SHAPE on it unless you have planned it out. And you do need to give them enough pixels to print well. Planning ahead to avoid surprises by first cropping the image to match that paper shape, and also to provide enough pixels so that the result will be 250 to 300 pixels per inch will be a very good plan.

  If your image dimensions are too large, the photo shop will first resample it to this smaller requested size. That's not necessarily a problem, except a far too-large image will be slow to upload. Or, if too small (insufficient pixels provided), the print quality will be lower, and the lab may refuse worst cases. But if the provided image shape does not match the paper shape, the excess image outside the paper edges simply disappears, and results may not be what you expected (like the heads-cut-off problems you may have seen).

• If printing yourself at home, the Print menu in your photo editor normally does use the file's scaled image dpi number (pixels per inch) to size the images on paper (regardless if it matches the paper size at all). But it typically will also allow changing that dpi, called scaling (to fit the paper size). For example, if an image dimension is 3000 pixels, then specifying that file number as 300 dpi printing resolution will print it to be 3000/300 = 10 inches print size (even if the paper is only 4x6). But the dpi number that your digital camera initially stores in the image file, unless you have reset it to your planned value, is otherwise far from meaningful, it is just some arbitrary number, which will print SOME size, but not likely to be your own printing goal. Hopefully, you have already properly scaled the image for your selected paper size.

  At home, most photo editors will also provide an option to "Scale to fit media" or "Best fit to page", which will scale the image to fit the specified paper size (similar to the labs above). This can be borderless if so specified in the printer Properties. This scaling will print at a new dpi which will fit the paper size. But it will not necessarily fit the paper "shape", which requires cropping attention done by you.

  Regardless if you print them yourself at home or send them to a one hour shop doesn't matter. You have to prepare them for print either way, in the same way. The purpose of this page is to describe what you need to know.

Images have both size and shape properties. The image "shape" (which is width / height, called Aspect Ratio) likely rarely matches the paper "shape", so which always needs attention first. When the print and paper shapes differ, a print shop "fit" typically fills all of the paper, fitting one dimension to leave no unfilled white space border in the other. A home photo editor "fit" typically is the opposite by default, not cropping at all, but leaving thin white space in one dimension if it doesn't fit precisely.

Either way, it is good if your plan properly prepares the image for printing. Sufficient pixels is important, but first cropping the image so that the image SHAPE actually matches the selected paper SHAPE is also a very important concern. Different paper sizes are different shape. And we need to provide the necessary pixels. The simple calculation for that acceptable image size for printing is:

(The actual dpi calculator is below). Here, this is all about SIZE, and does not yet mention about need to match SHAPE to the paper's SHAPE. This first simple calculator will serve these general purposes:

• Scanning: It calculates the scanned output image size created if the area is scanned at the dpi resolution.
  Scanning 10×8 inches at 300 dpi will produce (10 inches×300 dpi)×(8 inches×300 dpi) = 3000×2400 pixels. Your scanner program surely shows you the same information. Basically, scanning dpi basically just creates enough pixels so you can enlarge a small size (by printing it larger). For example (in general - speaking of any size original):

  Scan at 600 dpi, print at 300 dpi, for 600/300 = 2X size (to print double size or 200% size)
  Scan at 300 dpi, print at 300 dpi, for 300/300 = 1X size (to print original size or 100% size)
  Scan at 150 dpi, print at 300 dpi, for 150/300 = 1/2X size (to print half of original size or 50% size)

  Extreme dpi is for enlargement of small things. Scan small 35 mm film at 2700 dpi, print at 300 dpi, for 2700/300 = 9X size. If from full frame 35 mm film (roughly 0.9 x 1.4 inches), then 9X is about 8x12 inches (near A4 size). That is a proper goal.
  But caution, if you scan a 8.5x11 inch paper at 2700 dpi, you will have 2.045 Trillion bytes of image, which will be a huge problem until you delete it.

• Video monitors: Video does not use dpi, but scanners and printers do. The HD video screen is often sized to be 1920x1080 pixels (16:9, or 1.78:1). If you scan a 6×4 inch print at 100 dpi, it will create a 600×400 pixel image, and regardless of screen size (in inches), the monitor will show it at that same 600×400 pixel size.
• Printing: Dpi calculates the required image size (pixels) to print this image size (inches or mm) on paper at the dpi resolution. 10 inches at 300 dpi is 10×300 = 3000 pixels.
  3000×2400 pixels printed at 300 dpi will print (3000 pixels / 300 dpi)×(2400 pixels / 300 dpi) = 10x8 inches on paper.  The full meaning is if you want to print 8×10 inches at 300 dpi, then you need 2400×3000 pixels. See a Printing Guidelines page.

  For any image, if you specify an 8x10 inch print at the one hour print shops, you will get 8x10 inches regardless of what image content area they have to crop off to to do it, if the paper and the image are not the same shape (same Aspect Ratio). But if you crop it to the right shape first yourself when you can see what you're doing and choose the final view, there will be no surprises. This is Not much burden, it is selecting the best choice. And also quite important, adjusting cropping a bit more often improves many images by eliminating objectionable areas, even such as the blank wasted space surrounding the subject, but that adds nothing you want to show. That crop also makes the subject larger in the final frame.

• Copies

  At home, if you both scan and then print at the same dpi, it will print a copy at the same original size. 300 dpi will be a great number for a high quality photo print. Photos are best printed at 300 dpi on a photo quality printer and on actual photo paper. Black and white text pages are a bit better at 600 dpi.

  Scanning to print a copy at the same size is a very common goal. It's important to realize that an area scanned at 300 dpi will create the pixels necessary to also print the same size at 300 dpi. And 300 dpi is likely what you want for a photo copy job.

  Enlargement is done by increasing the scan resolution. For example, scanning at 600 dpi will give sufficient pixels to print 2x larger at 300 dpi. Scanning at 600 dpi, printing at 300 dpi will be double the size in inches. Or scanning at 150 dpi and printing at 300 dpi will be half size.

  The one-hour print shops will be different. They do accept larger images, and will crop to any shape you specify, ignoring the picture content. So if you want to define the expected picture content, you will need to first crop it yourself as desired. Many of their machines are set to use 250 dpi, which should be very satisfactory.

But this dpi number does NOT need to be exact, 10% or so variation won't have great effect on quality. Just scale it to print size. But planning size to have sufficient pixels to be somewhere near the size ballpark of 250 to 300 pixels per inch is a very good thing for printing photos. However an exception: Black & White text documents or line art (one color of ink or blank) can be improved at 600 dpi.

Aspect Ratio - a Printing Basic about image "Shape"

Long dimension fitted	Short dimension fitted
The calculator uses the Short or Long nomenclature You can try both, but there is an actual real solution

Preparing the image shape to fit the paper shape is necessary, because paper and image are often different shapes.

Aspect Ratio is the SHAPE of the image — the simple ratio of the images long side to its short side, which is a shape, maybe long and thin, or short and wide. Image aspect ratio is important, to properly fit on the paper (or in an area on it or the HD TV screen). We generally must crop the image to fit the paper, to know it is going to fit. Every paper size seems to be a different shape too. Shape and size are two different properties. To print an image, we can always enlarge the Size, but the image shape needs to match the paper shape (which is done by cropping). If this Aspect Ratio is a new subject, see Image Resize - Aspect.

It's necessary to crop the image shape to fit the paper shape, because otherwise the printer will crop it in surprising ways. When you crop it first, then you get what you wanted. Size is easily adjusted, but shape can only be cropped. You could wait for the printer machine to simply trim the image automatically (leaving whatever actually fits on the paper shape, without regard to the subject), but you will like the results better if you first choose the cropping yourself. It should be obvious that the shape of an 8x12 inch image simply cannot be fully fitted onto 8x10 inch paper. See Image Resize about how to plan this necessary resize and/or crop (specifically the second page there which has specific instruction about cropping image to match paper shape). That usual procedure is, FIRST crop image to paper SHAPE, and then resample image size to fit paper SIZE. Otherwise, printing will just cut off the part of the image that won't fit on the paper. Which could be a surprise you probably won't like. 😊  But this is all easy to do right.

Printing and Scanning DPI Calculator

If the image was previously cropped to be the same aspect ratio as the selected paper shape, then great, that's the idea. If not, the calculator will advise what the optimum cropped size should have been. Most one hour print shops won't leave any white space, and this calculator can do the same. However, before you print it, it would always be a really good thing if you had first prepared the image to fit the paper properly, both shape and size.

Scanning common film and paper print dimensions will be in the Scanner "Area" box below. Or you can specify any scan or print size.

Clicking a Compute button scrolls the screen down to the results, but if this jumping is objectionable, you can turn scrolling off.

Description of Above Results

If the Result text might not be meaningful yet, then start at this: Cropping, Resampling, Scaling. It's the basics of something we all need to know about printing images. The idea is not to simply compute some numbers, but to try to explain how you can already know this yourself. It's actually pretty simple.

Caution: When cropping and resampling your image for printing purposes, you should always save your original image for any future plans, because we do change our minds, but there's no going back. So always save such edits into a new file name. Don't overwrite your original image file, because then it is gone.

Your image aspect ratio rarely matches the paper aspect ratio, so more results are offered:

1. The first thing to know is that in order to NOT CUT UP your original image, FIRST crop a COPY of the image to the same aspect ratio as the paper print will be, or that the 1920x1080 pixel HD TV screen will be. You can also make that same crop seriously improve the image composition, by cutting out any blank (uninteresting) space at the edges that does not show anything, and/or you can cut out any distracting elements, but the image being the correct shape to fit the display media is the main idea.
2. It shows what your current numbers wants to print at literally whatever resolution it computes (but if no better action is taken, it likely still does not match the print paper shape). This is also what you would get now at the one hour photo lab (as much as the surprising crop on the actual paper size can provide). Can't be done proper without some attention first. The one-hour print lab is not expected to handle the "crop to shape" in any good way that would please you, because humans don't see it. Their automated printer machine does it today, which simply doesn't see or recognize your image content. It just cuts off whatever won't fit on the paper, which simply disappears. It's your job now, to crop to show it how you want to show it.

   Possible text suggestion in the scanning options: The computed scan resolution for film possibly can result as like 2540 dpi, closely missing one of the scanners default multiples of 300, 600, 1200, 2400, 4800 dpi. It will show and use that number, but if the miss is pretty close and might be considered negligible, the calculator might also suggest for example, that scanning at 2400 dpi (instead of 2540) would still print the same size at perhaps 283 dpi, which likely cannot be distinguished from 300 dpi (see next page). Many one hour labs limit printing to 250 dpi anyway (but their continuous tone is better quality than an ink jets dithered reproduction). Again, it is just an alternate suggestion to be aware and possibly consider. You can also get the same information for different multiples in Option 3 by just trying a couple of values of available resolution.

3. The suggested pixel dimensions for the largest possible "crop to shape" are shown first, but that would be awkward to measure directly. Instead there are better tools that mark an aspect ratio shape. "Any suitable crop" means best crop size and location that pleases you, to help your image look its best, but of the specific paper aspect ratio matching that paper shape. More details next page. That is probably different numbers than this first maximum, but that's no problem (within reason), feel free to crop your image tighter, to make it look best, but still matching paper shape. Camera images will likely still be much larger than needed for printing, but doing only this "Crop to fit paper shape" step should print satisfactorily. But large files are slow to upload and harder to handle (the print lab will have to resample it to acceptable size). Most print labs can deal with the large size, which can then still print properly after resampling (if it fits the paper shape). But excessively large is no advantage and serves no purpose for printing, and there are better choices.

   Both Size and Shape are important, and while you're dealing with "crop to shape", why not also resample it to a much more reasonable size first? (see below).

4. The best plan is to FIRST crop a COPY of the image to the shape to match paper shape (same aspect ratio). In good crop tools, there will be an option to specify your desired aspect ratio, and then any crop box you can mark will be the proper shape. Simply choose the best crop size and position of the area in that crop box for best image presentation and appearance, to show what you want the image to show (think about it a second, and choose the crop area to omit the distracting or empty uninteresting areas, and keep the best view). If the paper is 5:4 aspect ratio, select the 5:4 ratio for the crop, so that box will be the correct paper aspect ratio.
5. Any yellow calculator result section is just comments, hopefully instructive.

Second page   Printing basics that will be good to know.

Image Size is absolutely only about pixels, but file compression or the image mode of Color, or Grayscale, or Line art, or Indexed color, or Raw, all will make a big File size difference (bytes). See a calculator that will show these four sizes.

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