The aspect ratio of a camera sensor or format is simple to understand, though confusing at first.

Here’s a quick video for beginners that will help you understand what it is, and how to choose the right aspect ratio for your work:

Exclusive Bonus: Download my free cheatsheet (with examples) of the most used focal lengths in film (PDF file optimized for mobiles and tablets).

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What is Aspect Ratio?

Aspect ratio is simply the horizontal length divided by the vertical breadth:

Aspect Ratio = Length (of sensor/format) / Breadth (of sensor/format)

Why sensor/format? What does that mean?

The sensor is a fixed rectangle. It has a fixed length and breadth. Let’s take the Arri Alexa for example:

Arri Alexa XT/SXT Formats Length Breadth Aspect Ratio Or
Sensor Image Size 23.76 17.8 1.33 4:3
Sensor Max Resolution 16:9 2880 1620 1.78 16:9
4K 3200 1800 1.78 16:9
3.2K 3200 1800 1.78 16:9
2K 2868 1612 1.78 16:9
1080p 1920 1080 1.78 16:9
4:3 Anamorphic Mode 2880 2160 1.33 2.67:1
6:5 Anamorphic Mode 2880 2410 1.20 2.39:1

As you can see, a high-end cinema sensor can offer multiple formats. In addition, those who want 1.85:1 or 2.39:1 can crop their 16:9 image.

DSLR and mirrorless cameras usually only offer 1920×1080 or 3840×2160, or 16:9. Check the specifications of your preferred camera thoroughly.

Aspect Ratios for common scenarios

Here are the most widely used aspect ratios for your reference.

Most widely used aspect ratios for Distribution
Youtube/ Internet Video/ Netflix 16:9
Vimeo Variable but 16:9 default
Cinema 1.85:1
Cinema “anamorphic”* 2.39:1
Academy 1.375:1
Another version of academy 4:3
Still Camera DSLRs 3:2
Some mirrorless still cameras 4:3
New Phase One IQ380 100 MP 4:3
4×5 Large format 1.25:1
8×10 Large format 1.25:1

*You can either shoot 4:3 (or 6:5 as the new Arri Alexa SXT) and use an anamorphic 2x lens to get 2.39:1, or shoot 16:9 and crop to 2.39:1. Both are acceptable methods.

How to choose the right aspect ratio

Simple! Pick the aspect ratio that matches your delivery format. Where do you want to show it?

Sometimes it’s not so simple. What if you want to shoot a movie to project in a theater, have Blu-rays made, stream it on Netflix and maybe show it on television?

In this case, pick the most important delivery format first. For most movies it’s the theater. Many movies go “straight to DVD” or is “made for television”. You’ll have to take your best educated guess before you commit to one aspect ratio.

Picking the right aspect ratio is crucial, as it will save you a lot of time and hassle later on.

Pixel aspect ratio

This is another thing altogether. To understand this, read What is aspect ratio and pixel aspect ratio?

I hope this simple explanation of the aspect ratio has helped you understand and navigate it. Please feel free to ask me any questions in the comments below.

Exclusive Bonus: Download my free cheatsheet (with examples) of the most used focal lengths in film (PDF file optimized for mobiles and tablets).

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