What is aspect ratio in photography and why is it important?

When we talk about aspect ratio in photography we’re referring to the dimensions of an image. Or, to be more exact, aspect ratio is the proportional relationship between the width and height of an image.

Sounds boring and technical, but understanding aspect ration is really important to understand if you want to post your photos online or print them.

The only time it doesn’t really affect you is if you only look at your photos on your computer and never share them anywhere.

Do you watch TV?

It’s just like when you watch an old TV series on your modern TV – you’ll see black bars on the top, bottom or the sides of the TV screen.

Television screens used to be squarer than they are now, so old programs were made to fit those screens. They have different aspect ratios.

Now we have wide screen format and even computer monitors have changed shape.

Portrait photo using 3:2 aspect ratio
The standard aspect ratio of a digital image or 35 mm film image

A client confused by print sizes and aspect ratio

Years ago I had a complaint from a client who wanted to create a print of the digital images that were included in her package. She called me up to say there was something wrong with the photos, because when she printed them some of the image was missing.

She printed them a second time, but bigger, and the same thing happened.

I asked her what size she was printing. It was for an 8×10 frame. The photo was a standard size from a full frame digital camera. So the digital image wasn’t the same shape as the print she wanted. In other words they had different aspect ratios. 

I tried to explain to her that the image couldn’t be printed for that size frame without cropping off 2 inches from the longest side. It could, however be printed without cropping at 8×12 inches.

She wasn’t happy with me, replying that as a professional photographer she thought I would provide images that she could print in whatever shape she wanted.

I pointed out that to make a round print, for example, she’d have to cut off the edges to fit the round shape. And it works the same way with other shapes.

What I learned from this exchange was that many people don’t understand how aspect ratio in photography works. And that’s probably true for new photographers as well.

After all, if the aspect ratio of an image is confusing for photographers, it must be completely mind-blowing for anyone not interested in photography.

So let’s break it down…

What’s the aspect ratio of digital cameras?

In digital photography, the aspect ratio of your sensor determines the aspect ratio of the digital image. In film photography the type of film determines the aspect ratio. For both digital photography and 35mm film photography, the aspect ratio is 3:2.

I should clarify and say that for most digital cameras, regardless of sensor size (i.e. crop frame or full frame sensors), the most common aspect ratio is 3:2. However:

  • Medium format cameras have an aspect ratio of 4:5
  • Smart phones and micro four-thirds cameras have an aspect ratio of 4:3

So for most of us it means that we can create the following print sizes without cropping off part of the image:

  • 6×4
  • 9×6
  • 12×8
  • 24×16

Etc, etc.

If these sizes sound unfamiliar to you, it’s because for some reason the printing world hasn’t caught up with 35mm film yet, let alone digital camera sensors of both DSLR cameras and mirrorless cameras.

Why aspect ratio matters when printing

I don’t know why, but most printed products are still offered in the 4:5 ratio of medium format cameras used exclusively by professional photographers decades ago. The medium format image is shorter than images created by most digital cameras today.

Standard frame sizes (in USA, UK and a few other countries) are:

  • 8×10
  • 16×20
  • 24×30

Etc, etc.

It’s clearly not helpful that the standard aspect ratios of digital files are different from the standard aspect ratios of print frames. So what do you do if you have to print for one of these outdated standard size frames?

You crop off part of your image, just like you have to crop your vertical orientation images for Instagram.

We’ll get to how to work out the crop the height of a photo in a minute. Let’s first look at why we should care…

Aspect ratio and social media platforms

If you’re thinking that aspect ratio doesn’t concern you, because you don’t print photos, think again. Aspect ratio is very relevant when posting to social media.

Ever had a really great, perfectly composed portrait orientation photo that you tried to post to Instagram?

Either the top or the bottom of the image has to be chopped off, because the Instagram portrait aspect ratio isn’t the same as the aspect ratio of an image.

Aspect ratio in photography settings
The first number is the width of the image and the second number is the height of the image

Instagram is a perfect example

As a perfect example of how social media platforms have their own specific aspect ratios for digital images, here are the different sizes Instagram uses:

  • Instagram grids display square format photos. In other words they have a 1:1 ratio – both sides are the same.
  • Vertical images in Instagram are displayed at a 4:5 portrait aspect ratio, which is shorter than the actual height of the image taken by most digital cameras.
  • Horizontal images on the other hand display fine in the feed at 3:2 or 16:9.
  • Reels and Instagram stories suit a 16:9 aspect ratio, which is skinnier than the full size image your camera captures.

Losing your mind yet? Never mind your mind, this really messes with your composition!

Examples of vertical and horitzontal aspect ratios in photos
Left image: aspect ratios for a vertical crop. Right image: aspect ratios for a horizontal crop

Composition issues of different photography aspect ratios

Aside from printing issues, if you know that you’re photographing something that has to fit a 4:5 ratio frame or for Instagram, you need to make sure that you leave extra space around the edge of the image to allow for cropping.

If you don’t allow the extra space, you’ll have to crop off part of the image that you wanted included and this might spoil the look of the image.

Even worse – if it’s a group image, and you haven’t left enough space to allow for cropping, the people on the edges are in danger of being cut out or cut into.

How composition can go wrong…

If you composed an image carefully in camera using the rule of thirds and it looks perfect. But didn’t think about where that image was going to be used or what size it would be printed. By the time you crop it to fit where it’s going, your rule of thirds composition could be out of whack.

I always get caught out when posting vertical orientation images to Instagram, because I photograph with printing the full image in mind, not for social media platforms.

I compose an image according to what I can see through the viewfinder. So when I post vertical images to Instagram, I have to sacrifice my composition to fit the platforms default aspect ratios.

Further reading: Cropping portraits for flattering results

Cropping photos for their intended use

Now that you see why aspect ratio is important, you know you need to think about the image’s intended use when capturing photos.

But you’re probably wondering how to crop an image for the best aspect ratio for social media or printing for standard frames.

You have two options…

Lightroom custom aspect ratio tool
Square format image with a 1:1 aspect ratio

1. The easy way to work out where to crop

In Lightroom you can input custom dimensions to change image size and crop to the aspect ratio you want.

In the Develop Module:

  • Click R to open up the crop tool
  • Click the double triangles next to the lock
  • Scroll down to “Enter Custom”
  • Enter the sizes you want

Once this is set, when you drag from the corner to crop the aspect ratio will remain the same.

Crop overlay showing photo aspect ratio
Lightroom crop overlay showing where to crop for the most commonly used aspect ratio options

While we’re on the subject of cropping in Lightroom…

There’s a really easy way to see what a photo will look like with the 3 most popular aspect ratios for print:

  • Open the the crop overlay tool (click R)
  • Cycle through the overlays (click O to change overlays) until you get to the overlay you see in the image above

Further reading: Cropping in Lightroom – essential cropping, resizing and straightening tips

But not everyone has Lightroom and even if you do have it, you might need to work out the dimensions of an image when you don’t have Lightroom to hand.

2. How to manually work out the 4:5 aspect ratio in photography

I’m using 4:5 as an example, because this particular aspect ratio is so popular for printing. Plus, Instagram uses it for vertical images.

Of course there are many other aspect ratios for photos, including:

  • A square image has an aspect ratio of 1:1.
  • A panoramic image (wide and thin) has an aspect ratio of at least 2:1 – in other words, it’s least twice as wide as it is tall.

To create an image to fit the 4:5 dimensions, we have to crop off either the:

  • Top or bottom of a vertical image
  • Sides of a horizontal image

For an 8×10 inch print (a very common print size) 2 inches will have to be cropped off to fit a 4:5 ratio frame. If you print the image as your camera captured it, it would be 8×12 inches.

Stick with me – this will make sense.

How do you know if a frame’s aspect ratio is 4:5 or 3:2?

Here’s an easy trick for when you’re looking at frames wondering which one would fit your full image as you captured it:

  • Divide the shortest side by 4
  • Divide the longest side by 5
  • Do you get the same number?
  • Yes – it’s a 4:5 aspect ratio
  • You’ll have to crop the image
  • No – it’s not 4:5


  • Divide the shortest side by 2
  • Divide the longest side by 3
  • Do you get the same number?
  • Yes – it’s a 3:2 aspect ratio (vertical) or 2:3 aspect ratio (horizontal).
  • No cropping required

For example…

A frame is 30×20

Divide 30 by 3 = 10
Divide 20 by 2 = 10
Yes, it’s a 3:2 aspect ratio

A frame is 18×12

Divide 18 by 3 = 6
Divide 12 by 2 = 6
Yes, it’s a 3:2 aspect ratio

Over to you…

What aspect ratio is a 24×30 inch frame?

Divide 24 by 2 = 12
Divide 30 by 3 = 10

Not a 2:3 ratio. Try again.

Divide 24 by 4 = 6
Divide 30 by 5 = 6

Answer: It’s a 4:5 aspect ratio. You’ll have to chop off part of the original image.

What is the best aspect ratio in photography?

Many portrait photographers will say that 4:5 is the best portrait aspect ratio. I disagree, I prefer a 3:2 aspect ratio for portrait photography – the full size image my camera produces. I find it elongates my portrait subject.

That said, for some of my images 4:5 is the best aspect ratio.

Landscape photographers also prefer 3:2, but many create panoramic images using a 2:1 aspect ratio.

If you’re not restricted by print size or social media dimensions, the best aspect ratio to use is determined by subject, composition and personal choice.

The best aspect ratio for photography is the one that suits the image.

Leave a comment

If you have any questions about aspect ratio in photography, let us know in the comments.

Also, I love good news, so if my photography tips have helped you to understand how to choose the best portrait aspect ratio, share that too.

3 thoughts on “What is aspect ratio in photography and why is it important?”

  1. I hate when they try and stretch an old tv picture to fit a modern screen
    I comment to my kids and they don’t see it. I say what do you mean you don’t see it?
    The people look fatter the cars are too long and the tires aren’t round.
    They still don’t see it!

  2. This is the only educational article I’ve found on aspect ratio and how it relates to printing and framing that explained a complicated subject very thoroughly. Excellent job spelling it all out in detail. I ‘get it’, but will refer to your article again and again. Thank you!!


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