The most popular facebook ad size is 1200 x 628 pixels. The image cannot contain more than 20% text. One exception is if the image (or photograph) contains a product or object that has text on it naturally. The 1200 x 628 recommended facebook ad size will get resized once it is uploaded.
Facebook uses a very primitive way to calculate how much text is in an image. Facebook uses a 5x5 grid overlay on the image and sees which boxes contain text out of the 25 boxes. Even if there is a bit of text in a box, Facebook counts that box as containing text.
For example, if 5 of the 25 boxes have text in them, you meet the requirements (5/25 is 20%).
Best Facebook Ad size
Recommended Image Size: 1200 x 628 pixels
Image Ratio: 1:9:1
Minimum Resolution: 470 x 246 pixels
Canvas cover: 1200 x 628 pixels
Carousel Images: 1080 x 1080 pixels
Slideshow: 1280 x 720 pixels
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