How to change aspect ratio in Midjourney
What is aspect ratio?
How to use the aspect ratio parameter --ar
Aspect ratio ranges and limitations in MidJourney
Changing aspect ratio using the remix setting
Aspect ratio summary and tips
What is aspect ratio?
Aspect ratio is a simplified way to describe the dimensions of an image (width and height). An aspect ratio does not tell you the size of the image in pixels, but rather how the width and height of an image relate. Aspect ratio is written as width:height. An image with an aspect ratio of 1:2 means that the height of the image is twice the width or that the width of the image is half the height. The image itself could be 100 x 200 pixels or 1200 x 2400 pixels. Both of these image dimensions would still be reduced to an aspect ratio of 1:2.
How to use the aspect ratio parameter --ar
The default aspect ratio for Midjourney images is 1:1. In other words, a square. To change the aspect ratio, add the parameter --ar followed by a space to your prompt and then enter your desired aspect ratio in width:height format.
Here, I typed in /imagine wizard in the mountains --v 4 --ar 2:3 and pressed enter to submit my prompt. The --v 4 indicates I want to use the v4 algorithm. The --ar 2:3 tells it that I want an image with a 2:3 aspect ratio.
Here is what the prompt looked like in Discord right before I submitted it. If you are new to Midjourney and/or would like a summary of the basics, please check out my Beginner's Guide to MidJourney.
Below are the results of my prompt. Each image in the grid of images has an aspect ratio of 2:3.
Grid results for /imagine wizard in the mountains --v 4 --ar 2:3
Upscaled result for one of the grid images
If it is easier for you to think in terms of familiar image sizes such as 1024 x 768 pixels, you can use --w and --h (except for when using the v4 algorithm) instead of --ar to specify an aspect ratio. For example, you can enter --w 1024 --h 768 at the end of your prompt instead of using the --ar parameter. It will not give you an image with size 1024 x 768 pixels, but it will use those numbers as an aspect ratio. An image that is 1024 x 768 pixels has an aspect ratio of 4:3. That said, I recommend sticking with using --ar whenever possible.
Aspect ratio ranges and limitations in Midjourney
Each Midjourney algorithm has a pre-determined set of aspect ratios available. A square aspect ratio (1:1) is the default across all algorithm versions. What can vary among the different versions is how far you can stretch one side of the image to make a skinnier and skinnier rectangle. For example, the v1 algorithm allows aspect ratios out to 2:7 and 7:2, whereas v4 only allows up to 1:2 and 2:1 aspect ratios. Commonly used non-square aspect ratios include: 2:3, 4:5, and 9:16.
What aspect ratios are available in Midjourney?
The tables below contain the output aspect ratio that you will get, based on the input aspect ratio you provide. If an aspect ratio is unavailable for a particular version of Midjourney, it will use an aspect ratio that is available and is the closest match to your input.
I submitted prompts using 14 different aspect ratios in both portrait and landscape orientations across all Midjourney algorithms. The first column in each table contains my input aspect ratio. Then, by Midjourney version, each cell is filled in with the aspect ratio that I observed in the image grid returned by Midjourney. The rows are sorted by square to least square input aspect ratio. Blue cells are where the output aspect ratio matched the input aspect ratio. Orange cells indicate the output aspect ratio did not match the input aspect ratio (although in some cases they are very close). The dashes in the v4 and niji columns indicate aspect ratios where, if used, they will result in an error.
Portrait style aspect ratio results in MJ grid output based in input aspect ratio and version. *Not exactly, but very close
Landscape style aspect ratio results in MJ grid output based in input aspect ratio and version. *Not exactly, but very close
Nuances to be aware of
The 9:16 aspect ratio is popular for things like smartphone wallpapers, Instagram reels, TikTok videos, etc. In the tables above, you'll see that using --ar 9:16 will return an image with a 4:7 aspect ratio. Do not panic. These two ratios are actually very similar. We can see how similar these two ratios are by dividing the width and height values. 9/16 = 0.5625 and 4/7 = 0.5714. Therefore, converting the output 4:7 image to 9:16 requires minimal cropping.
Midjourney Aspect Ratio Reference Document: https://woollyfern.gumroad.com/l/midjourney_aspect_ratios_table
What if you submit an aspect ratio that isn't in the tables above? Midjourney will pick the closest available aspect ratio to the one you requested. What aspect ratios are available depend on which version of MidJourney you are using.
For example, I submitted the prompt /imagine wizard in the mountains --v 3 --ar 1:10. The aspect ratio 1:10 is a fairly skinny rectangle. The skinniest aspect ratio available in v3 is 2:5. Thus, my output images had a 2:5 aspect ratio rather than 1:10.
Changing aspect ratio using the remix setting
You can, sort of, change the aspect ratio of an image you like. Let's say you just generated a really cool square image, but you want to alter the aspect ratio without cropping the image. Midjourney has a setting called "Remix" that, when enabled, allows you to alter the prompt text when you "re-roll" or make variations on an image.
First you need to make sure you have the setting enabled. In Discord, type in the command /settings to bring up your default settings. Make sure that you have "Remix mode" selected in your settings. Once this is selected, every time you click the "re-roll" button, you will get a pop-up where you can change the prompt text, if desired.
To demonstrate this, I submitted the prompt /imagine wizard in the mountains --v 4 and got the grid of square images shown below.
I liked the image in the lower right, so I clicked the "V4" button to make variations on that image. After clicking "V4", I got the pop-up message below. Then, I added --ar 2:3 to the end of text prompt and clicked Submit. Midjourney gave me a new grid of 4 images with a 2:3 aspect ratio, using my original image as a reference image. What is most noticeable is that the resulting images appear stretched compared to the original square image. The remix feature does not add canvas space to your original image. It is a stretching tool. With additional re-rolls and perhaps some slight prompt tweaking, I would be able to get closer to the original wizard, if that's what I wanted.
Remix results
Aspect ratio summary and tips
Check out my Beginner's Guide to Midjourney here!
Midjourney has a guide to understanding image size
Just because the --ar value you used did not result in an error, doesn't mean your image will have the exact aspect ratio requested. Midjourney will pick the closest match available.
Try not to be discouraged if your specific aspect ratio is not available. Work with the closest available aspect ratio and crop your output image as needed.
When you upscale an image with Midjourney, this will occasionally, very slightly, alter the aspect ratio of the upscaled image. This is dependent on the Midjourney version and what upscaler is being used. I recommend checking your final image and crop it if needed.