Aspect Ratio: What it is and Why it Matters

Aspect Ratio: What it is and Why it Matters

Aspect ratio

This article is written by Andrew S. Gibson, the author of Square.

Today I’d like to draw your attention to an area of composition that you might not have given much thought to: aspect ratio.

Aspect ratio is the term used to describe the dimensions of an image by comparing the width to the height and expressing it in ratio form.

The aspect ratio of your images is primarily determined by the dimensions of your camera’s sensor (or the film type plus camera design with film cameras). As these physical aspects are fixed, it is easy to take the aspect ratio of your images for granted, and to not consider the implications of the aspect ratio you are using in relation to composition.

Camera makers have realised that sometimes photographers like to work in different aspect ratios, and most recent digital cameras let you change the aspect ratio using the camera’s menu. You can also crop an image to a different aspect ratio in post-processing.

Why aspect ratio matters

Why does aspect ratio matter? It’s all to do with the relationship of the main subject to the sides of the frame, and the amount of empty space you end up with around the subject.

An awareness of the characteristics of the aspect ratio of your particular camera can help you compose better images. It also helps you recognise when cropping to a different aspect ratio will improve the composition of your image.

What is aspect ratio?

Aspect ratio describes the relationship between the width and height of an image. It’s written as a figure, in this form – width:height (width always comes first).

Virtually every digital camera comes with a sensor of one of two aspect ratios:


Aspect ratio

An aspect ratio used by 35mm crop sensor and full-frame SLRs, some Leica medium format cameras, mirrorless cameras, high end compacts and most 35mm film cameras. This aspect ratio has been with us ever since Leica made the first 35mm film cameras early last century.

35mm crop sensor and full-frame SLRs have an aspect ratio of 3:2. The sensor is 1.5 times as wide as it is high.

A full-frame 35mm sensor measures 36 x 24mm. You can express this figure as a ratio: 36:24. Mathematicians always like to simplify ratios so that the relationship between the two numbers is easy to visualise. In this case, you can divide both dimensions by twelve. That gives you 3:2.

Crop sensor cameras have smaller sensors, measuring approximately 22.5 x 15mm (the exact measurements vary, depending on brand and model). These figures conform to the 3:2 aspect ratio of the full-frame sensor.


Aspect ratio

This aspect ratio is used by micro four-thirds cameras, many compact cameras, some medium format digital cameras plus medium format film cameras using the 6 x 4.5cm format.

Let’s compare the two:

Aspect ratio

You can see that the 3:2 aspect ratio used by most digital SLRs is slightly longer than the 4:3 micro four-thirds frame. This may not seem like much, but it has great implications for composition. Take a look at the following images to see why. Here’s the original, 35mm version with a 3:2 aspect ratio:

Aspect ratio

And here’s the same image cropped to the 4:3 aspect ratio, as if it had been taken with a micro four-thirds camera:

Aspect ratio

Do you see the difference? It’s subtle but it’s there. The 35mm frame is longer. And that can be challenging when it comes to composition, because you have to find a way of filling that length effectively. Landscape photography in particular often benefits from a shorter frame, and that’s one of the reasons for the popularity of the 6x7cm medium format (7:6 aspect ratio) and 5×4 view cameras (5:4 aspect ratio) amongst landscape photographers that use film cameras. Here’s what the same landscape would look like cropped to these formats:

Aspect ratio

Aspect ratio

For me, the 7:6 aspect ratio is too short, but 5:4 is a very pleasing aspect ratio to work in.

Now, so far you may be thinking that the difference between aspect ratios is not a big deal. And often, when you are using the landscape format (ie. the camera positioned so that the frame is horizontal), the difference is minimal. It’s not so difficult to work within any of the above aspect ratios.

But change to the portrait format (a vertical frame) and it’s a different story. The 35mm frame suddenly becomes a lot harder to fill effectively, and the composition often benefits from cropping to a shorter rectangle. Here are some examples to show you what I mean:

Aspect ratio

Aspect ratio

Aspect ratio

The difficulty that I had with this landscape is that there was too much empty sky in the original image. I solved the problem by cropping to a shorter rectangle. The 4:5 aspect ratio seems to work nicely.

Of course, not all images will benefit from a crop to a shorter rectangle. But if you find yourself struggling to fill the frame, especially if you have a 35mm camera with the 3:2 aspect ratio, then it may be a sign that you would benefit from using a different aspect ratio.

Adventure and landscape photographer Bruce Percy has written an interesting article on this topic.

Out of interest, here is the first image cropped to a couple more common aspect ratios. They are the panoramic format (16:9) and the square format (1:1)

Aspect ratio

Aspect ratio

Adjusting aspect ratio in-camera

Many recent digital cameras give you the option of adjusting the aspect ratio using the camera’s menu. If you have a camera with an electronic viewfinder, it may be able to display the cropped image in the viewfinder.

If your camera doesn’t have an electronic viewfinder, you will need to use Live View mode in order to take advantage of the aspect ratio function. The camera will display the cropped image on the camera’s LCD screen.

Whichever option your camera has, you should be aware that if you use the JPEG format, the camera will crop the image. You won’t be able to retrieve the cropped part of the image. If you use Raw, the camera will save the image as captured by the entire sensor, and you can change your mind about the crop in post-processing. Check your camera’s manual for details if you have any doubts.

Cropping in post-processing

It’s often easier to crop in post-processing than in the field. If your camera doesn’t have an aspect ratio function it’s the only way you can do it. Another benefit is that you can go back to old images to see if they would benefit from cropping.

If you have Lightroom, cropping is easy. Just click the Crop icon and select an aspect ratio from the list provided:

Aspect ratio

If you have Photoshop CS/CC, the Crop Tool in ACR works in a similar way:

Aspect ratio


Aspect ratio

My ebook Square explores the square format from the digital photographer’s perspective. It shows you how to use the square format on your camera, and how to make the most out of what I think of as the fine art photographer’s format.It’s available here for a special price for a limited period.

Read more from our Tips & Tutorials category

Andrew S. Gibson is a writer, photographer, traveler and workshop leader. He's an experienced teacher who enjoys helping people learn about photography and Lightroom. Join his free Introducing Lightroom course or download his free Composition PhotoTips Cards!

Some Older Comments

  • Sam July 26, 2013 01:41 pm

    Going to check my camera. I didn't even realized it was possible. Thanks!

  • Ron Thomas July 24, 2013 07:35 pm

    Hi Seeing all the images has given me many ideas to what I would like to achieve, all of your Landscapes are in very interesting places ,We have similar locations in Cumbria Lakes Mountains ect,
    Reading your article on Aspect Ratio was most interesting I have been using 16.9 I am now going to try 3.2 just to see the difference on printing my Landscapes.
    I would have liked to seen the camera settings, ND Filters that you used, just as a guide,
    Many Thanks

  • marie July 23, 2013 11:52 am

    photography math is so confusing to me - this was great! it helped quite a bit :)

  • Zach July 23, 2013 03:41 am

    Does anyone know of a tool that takes an image and crops it to different aspect ratios automatically?

    That'd be great for deciding on a final aspect ratio.

  • AnZanov July 20, 2013 01:14 am

    Just bought your "SQUARE" book


  • marius2die4 July 19, 2013 06:37 pm

    Very good article. I also consider aspect ratio have a great effect on composition.

    Some of my pics:

  • DougS July 19, 2013 06:11 am

    Nice article, and something I relate to a lot since I find that I am always cropping my images in some way. Even this morning I snapped some pics of the sun rise and ended up cropping all of them to a different aspect ratio (4:5).

    One of them I even cropped to a vertical aspect from the horizontal shot. Mainly because I couldn't get the shot by holding the camera vertically at the time. (I may or may not have been operating a motor vehicle...)

  • Mandy July 19, 2013 02:01 am

    Andrew, thank you for the detailed article. Please elaborate on what you mean that a square shape is a fine art photographer's format. I'm still learning the basic terminology of things, and am very literal, so could you explain how the square shape is a fine art photographer's format, why it is preferred, and give an example or two of how and why it is and what it brings to fine art photography? I just got my camera a month ago and am learning as quickly as possible.

  • Steve July 19, 2013 01:08 am

    5x4 can be an important aspect ratio due to the popularity of 8x10" prints. If you have a 3x2 image on your web site and someone wants an 8x10 of it, they will need to crop it. If you provide a 5x4 crop of your image on your site, you take control of how it is cropped instead of leaving it up to the customer or processing lab.

  • christi July 17, 2013 02:00 am

    Very well written and concise. And useful. It seems like there have been too many "empty" articles lately by people just trying to get publicity or something. More of this type please, DPS.

    Thank you, Andrew, for the simplification and the lovely images.

  • javan July 16, 2013 11:52 pm

    Good article, concise and easy to understand. I would point out that choosing an aspect ratio is not the same as cropping, which I have heard some photographers say. I like to shoot square (1:1) and it is really helpful to have a camera that lets me choose this option becuase shooting "full frame" and then trying to crop to a square later is difficult. You are guessing at where the sides will be and if you misjudge than you may vae to crop from the top and bottom to main tian the square. Hope that made sense, anyway, thanks for the article, Andrew, I have your book "Square" and have enjoyed it.

  • raghavendra July 16, 2013 02:22 pm

    wow, thanks for explaining with images.
    you have simplified
    "Aspect ratio describes the relationship between the width and height of an image"
    It is simple and effective

  • Wayne July 16, 2013 07:08 am

    Don't forget about cinematic aspect ratio of 1:2.39, it can give interesting results when applied to certain photos.

  • Brian Fuller July 16, 2013 02:44 am

    I've always really liked the 3:2 format, but after reading this article I see how the 4:3 and 1:1 aspects can also create a stronger image.
    I used to crop according to my own feelings, but more and more I'm trying to create images that can translate well to either online, photo books, or some regular portrait ratio. This is quite difficult.