Today’s Question: I have a question around saving photo files for printing in various aspect ratios. I am clear what final print size are applicable for each of the standard aspect ratios provided in Lightroom (i.e. 4×3, 1×1. 3×2, etc.). However, I would like to also provide digital files of my images in an aspect ratio appropriate for printing using the ISO Paper Size (A1, A2, A3…A6) sizes. It is not clear to me what aspect ratio(s) I would need to use in order to provide files which would allow for printing in those sizes.
Tim’s Quick Answer: In my opinion the easiest way to enter the aspect ratio when cropping an image for an output size that is not listed as a standard crop aspect ratio is to use the actual paper dimensions of the paper size you intend to print to.
More Detail: I should hasten to point out that in general my recommendation is to crop based on your artistic preference for the image, and then print to fit the applicable paper size for that crop. This will, of course, possibly result in extra space around the image if the aspect ratio for your crop does not match the aspect ratio of the paper. But to me the artistic preference is more important when cropping than the aspect ratio of the paper you’ll print to.
Of course, sometimes you do want to crop to a specific aspect ratio, such as to fit a specific frame or print size. In those cases, you can crop a photo to any aspect ratio you’d like. The simplest way is to treat the units of measure for the output dimensions as the aspect ratio settings when cropping.
For example, you can get the specific dimensions of the ISO Standard paper sizes for A Series papers on this website:
When you find the specific dimensions in any unit of measure, you can simply use those dimensions as the values for the aspect ratio when cropping. For example, a sheet of A4 paper has dimensions of 210mm by 297mm. You don’t need to worry about the fact that these measurements are in millimeters, even if you’re accustomed to working with inches. You can simply set the crop aspect ratio to 210 by 297.
You could also, of course, convert to inches and set the aspect ratio to 8.3 by 11.7. The point is that you don’t need to worry at all about the actual units of measure. Instead you can focus on the relationship between height and width, entering the values based on any unit of measure as long as you maintain the correct ratio between height and width.
Note, by the way, that in Lightroom Classic, you can choose the “Enter Custom” option from the Aspect popup for the Crop tool in order to bring up a dialog where you can enter specific values for the width and height based on the aspect ratio to which you want to crop the image.