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Ask a Photo Nerd: What’s Aspect Ratio?

You’re on the prow of an ocean-going ship, surveying your destiny. A crack of lightning. The sky opens and a single photo drifts down from the sky as if carried on a thread. It asks you, “What’s my aspect ratio?” and then runs madly into the night. What is aspect ratio and how should you size up this deranged photo? We asked the Photo Nerd for his thoughts.

Understanding aspect ratio is an important part of cropping, resizing, and ultimately printing photographs. It’s a key element to getting an image to fit to a specific shape.

Aspect ratio is jargon for shape. It’s a way to describe how the width of an image relates to its height. Don’t run away yet! If the concept was crystal clear we wouldn’t be here.

For now, just know that aspect ratio means shape. Let’s start off easy, with a square.

The height and width of squares are equal. For every unit of height (pixel, inch, centimeter, etc.) there’s an equal unit of width. This is a one to one relationship.

Image by Mico Procissi.

A square aspect ratio is expressed as 1:1. Wow, easy.

Wreck-tangles ruin everything

Just as we were getting along, rectangles come in and start making things all math-y. Rectangles don’t have equal sides; one is always longer than the other. If the image is twice as wide as it is high, then the ratio between width and height is two to one. This is expressed as a 2:1 aspect ratio.

2:1 isn’t a super common shape, but sticking two squares together is useful for conceptualizing and getting use to units of measurement.

What’s a more common aspect ratio?

A more common shape for image editing is 2:3, which you might sometimes see expressed as 3:2. The order of the numbers aren’t super important; it’s their relationship that matter. 2:3 and 3:2 are the same ratio.

Image by Mico Procissi.

If you’re wondering when we’re gonna talk about 4:6 because you’ve got a stack of 4 x 6 paper burning a hole in your printer, your days of wondering are over. A 4 x 6 print is a 2:3 aspect ratio. Doubling the units keeps the same shape and turns it into something more recognizable: 4:6, the shape of 4 x 6 prints.

4:5, 8:10, or 16:20? They’re the same shape!

Doesn’t anyone notice this? I feel like I’m taking crazy pills.

A quick scan of your old math textbook would remind you that 8 x 10 can be reduced to its lowest terms by dividing both of those numbers by two. What you end up with is 4 x 5. 4 x 5 and 8 x 10 are indeed the same shape: they’re different sizes in terms of prints, but as far as shape goes, they’re the same.

To illustrate this, the following image has been segmented into both 4 x 5 and 8 x 10 units of measurement.

Image by Mico Procissi.

What’s your point, Nerd?

Long story long, aspect ratio just a way to express the shape of a thing; to describe how height and width relate to each other. You can transpose the numbers, make ’em bigger or smaller. As long as they maintain the same ratio, you’re describing the same shape.

If you’re only concerned with shape, you can put all this newfound knowledge to work right away. Maybe you just wanna fit an image to your 16:9 television screen. To do that, just open up the crop tool select 16 x 9 in the dropdown, apply and save. BOOM you just earned a merit badge, hoss.

But say you care about the size of the image as well as the shape. That, my friends, will be the subject of the next post in this series.

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Photo Nerd Anthony Procissi is a product manager at PicMonkey and a self-appointed photography know-it-all with a penchant for speaking in laymen's terms. He lives in Seattle with his beloved wife and adored daughter.