What is aspect ratio?
Aspect ratio is the relationship between an image's width and height, written as two numbers like 16:9 or 1:1. It describes the shape of the image, not its size, so a 1:1 square looks the same whether it is 500 or 5000 pixels wide. Matching the right aspect ratio stops platforms from cropping your image.
Common aspect ratios
1:1 is a square used for many profile pictures and feed posts. 16:9 is widescreen, used for video and thumbnails. 9:16 is full-screen vertical for Stories and Reels. 4:5 is a tall portrait that fills more of a phone feed.
Why it matters
Every platform expects a certain ratio. Upload the wrong shape and the platform crops it to fit, often cutting off something important. Resizing to the correct ratio first keeps you in control of the framing.
Try it yourself, free
Every tool runs in your browser. Your image never leaves your device.
Frequently Asked Questions
How do I change an image's aspect ratio?
Resize or crop it to the target width and height. A resizer that center-crops keeps the subject framed while changing the shape.
What aspect ratio should I use for Instagram?
1:1 for square posts, 4:5 for portrait posts, and 9:16 for Stories and Reels. See the Instagram size guide for exact pixels.