Tutorial – Learning About Aspect Ratio

A while ago I had a “Ask Me Anything” post and one reader wrote in to ask:

12. Micki asks “That age old ‘printing certain sizes’ question. Some say you have to crop to a specific size but what if I like the crop the way it is??? I was also told I would have to save for each size…. that could mean 2 or 3 saves for particular photos….. i’m so confused…. personally I should be able to crop the photo to the 2:3 or whatever dimension and I should be able to get 4×6, 5×7, etc.. prints from that without it ‘cutting’ some of the picture.
 
That is a great question, and a common one. Today I want to share my answer as it’s own post, one that you can refer back to whenever you need a little reminder 🙂 
 
What you’re really wondering about is ASPECT RATIO. It’s essentially the relationship between the width and height of the photograph. When you are cropping your photo to the 3:2 ratio, for example, you are cropping a relationship, not an actual specific measurement. Does that make sense? 
Let’s say that I have an image with a 3:2 aspect ratio. The actual size of this image in pixels can be 300 x 200, or 600 x 400,  or 1350 x 900. So long as the relationship between the width and the height is always 3 to 2, the aspect ratio does not change even though the size of the image does. The resolution can be different.
 
So, a 3:2 ratio will give you a completely different crop than a 5:7 ratio, for example. Here is an example chart of different common print sizes, and their aspect ratios:
 
Print Size Aspect Ratio
4×6 3:2
5×7 7:5
8×10 5:4
20×30 3:2
So, if you upload a photo that has a 3:2 ratio, but you want to print a 5X7 or an 8X10 print, you are going to lose some of your photo as it will have to be cropped. Let me show you an example.
This is a photo of my daughter. It currently has a 5:7 aspect ratio. Different cameras automatically produce images with different aspect ratios. Let’s say my camera produces photos at a 5:7 aspect ratio, like this one.  I could order a print as a 5X7 and it would appear exactly like the photo below.
But let’s say I wanted to print it as a 4X6, not a 5X7. Well, let’s see what happend when I try to crop the image in photoshop, using a width of 6 in and a height of 4in. 
 
Can you see the part at the bottom of the photo that will be cut off? That’s because a 4X6 photo has an aspect ratio of 2:3, NOT 5:7. 
If I wanted to order the print as an 8X10, what would happen?
Now I’m losing some off the side, because an 8X10 photo has an aspect ratio of 5:4, not 5:7. If you want the photos you are seeing to come out in print exactly the way you see them, you can either use a camera that automatically uses the same aspect ratio as the prints you order (eg. use a camera that produces image with an aspect ration of 3:2, if you order 4X6 shots). OR, crop the photos in a photo editing program BEFORE you order your prints. That way you can control what get’s cropped off your photo. There is no “one size fits all” ratio that works for every print size, unfortunately.

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