For portrait feed posts, Instagram prefers 4:5 (1080 × 1350).
Understanding aspect ratios
An aspect ratio describes the shape of a rectangle as width compared with height. It is written as two numbers separated by a colon, such as 16:9, or as a single decimal, such as 1.78:1. Two images with the same ratio have the same shape even if one is much larger: 1280×720 and 3840×2160 are both 16:9. To simplify a resolution, divide both numbers by their greatest common divisor, which is what AspectCalc does when you enter a width and height. Many real resolutions do not simplify to a tidy pair, so the tool also shows the closest well-known ratio.
Solving for width or height
If you know the ratio and one side, the other follows by cross-multiplying. New height = width × ratio height ÷ ratio width, and new width = height × ratio width ÷ ratio height. That is how you resize an image without stretching it, plan a video export or set the size of an embedded player. You can enter the original dimensions directly as the ratio, so 3000 : 2000 works as well as 3 : 2.
Common ratios and where they are used
16:9 is the standard for HD and 4K video, YouTube and most screens. 9:16 is the vertical version used by Reels, Stories, TikTok and Shorts. 4:3 was the shape of older televisions and is still used by tablets and many compact cameras. 3:2 is the native shape of most interchangeable-lens cameras and of 4×6 inch prints. 1:1 square images suit album covers and profile pictures, and 4:5 is the tallest portrait shape Instagram shows in the feed. Ultrawide monitors marketed as 21:9 are actually around 2.37:1, and cinema films are often 1.85:1 or 2.39:1.
Screens and prints
Screens are measured diagonally, so the same 27 inch label gives very different widths and heights depending on the ratio. The screen panel works out the real dimensions and, combined with a resolution, the pixel density in pixels per inch. For prints, standard paper sizes have their own ratios: 8×10 is 5:4, 11×14 is about 1.27:1 and 4×6 is 3:2. If your image has a different ratio, part of it will be cropped or the print will have borders. Everything is calculated in your browser.
Frequently asked questions
What size is an Instagram Reel?
1080 × 1920 pixels (9:16).
Can I post 16:9 to Stories?
Yes, but it shows with bars or is cropped.
What is the TikTok safe zone?
Keep text away from the bottom and right edges, where buttons and captions sit.
Is AspectCalc free?
Yes, with no sign-up or ads.
Are my sizes saved?
Yes, in this browser only.