What aspect ratios does Midjourney support?

Since v5 Midjourney accepts almost any aspect ratio you pass to --ar, from extreme panoramas to tall portraits. Earlier versions were limited to a handful of presets. Very extreme ratios (beyond roughly 7:1) can still produce repetition or stitching artifacts, so the tool flags when a ratio is unusually wide or tall.

How do I turn pixel dimensions into an --ar flag?

Divide both the width and the height by their greatest common divisor. For example 1920x1080 has a GCD of 120, giving 16:9. Midjourney does not render at your exact pixel count — --ar only sets the shape of the frame, and the model picks a resolution that fits that shape.

Does --ar control the output resolution?

No. --ar only sets the proportions of the image. Midjourney chooses the actual pixel resolution based on the version and quality setting. To get a larger file you upscale the result rather than passing a bigger pixel size.

What is the default Midjourney aspect ratio?

The default is 1:1 (square). If you do not include an --ar flag, Midjourney generates a square image. Pass --ar 16:9 for widescreen, --ar 9:16 for vertical/mobile, or any other ratio you need.

Why does my ratio look different from what I typed?

The calculator reduces your dimensions to lowest terms, so 1280x720 and 1920x1080 both display as 16:9 — they are the same shape. The decimal ratio shown beside it (1.778) confirms the exact proportion before rounding.

Midjourney Aspect Ratio Calculator

Midjourney’s --ar flag wants a clean width-to-height ratio like 16:9, not raw pixel dimensions. This calculator takes any width and height you have in mind and reduces it to the simplest whole-number ratio, formats the flag, and shows you the frame shape so there are no surprises.

How it works

The maths is simple but easy to get wrong by hand. The tool:

Finds the greatest common divisor of your width and height using the Euclidean algorithm.
Divides both numbers by that GCD to reach the lowest-terms ratio — so 1920 x 1080 becomes 16:9, and 1500 x 1000 becomes 3:2.
Formats the flag as --ar W:H exactly as Midjourney expects it.
Shows the decimal ratio (width ÷ height) and a live preview rectangle so you can confirm the orientation at a glance.

Because Midjourney v5 and v6 accept arbitrary ratios, you are not limited to presets — but the tool warns you if a ratio is extreme enough to risk tiling artifacts.

Tips and notes

--ar is shape, not size. It never sets your output resolution. To get a bigger file, generate at your chosen ratio and then upscale.
Common presets: 1:1 square (default), 16:9 widescreen, 9:16 vertical/stories, 4:3 and 3:2 classic photo, 2:3 portrait, 21:9 cinematic.
Avoid extremes. Ratios beyond roughly 7:1 can cause the model to repeat elements to fill the long axis. If you need a banner, generate at a moderate ratio and crop or extend.
Whole numbers only. Midjourney expects integers in --ar, which is exactly what the lowest-terms reduction produces.