Image glossary
Aspect ratio
Also known as ratio, image proportions
Aspect ratio is the proportional relationship between an image's width and height, expressed as two numbers such as 16:9, and it is what determines whether a platform crops your image.
Why it matters more than pixel count
Upload an image with the right shape at slightly the wrong resolution and the platform scales it, costing a negligible amount of sharpness. Upload one with the wrong shape and the platform crops it, using an algorithm that has no idea which part of your image carried the meaning.
That asymmetry is where every visible failure comes from: the headline sliced in half, the logo cropped out of a corner, the face cut off at the forehead by a square thumbnail. The platform is not being careless; it has been handed an image it cannot display and is taking the only action available.
The five that cover almost everything
1:1 square, for feed posts and profile grids. 4:5 tall portrait, the most vertical space an in-feed image is allowed. 9:16, full-screen vertical for stories and reels. 16:9 landscape, for video thumbnails and wide posts. And 3:1 or wider, for profile headers and page covers.
Platform-specific pixel dimensions churn constantly; these shapes are set by the shape of a phone and a monitor, and have not changed in a decade. Learning the ratios makes the pixel tables a lookup rather than a memory test.
Resolving a conflict
One image cannot be 4:5 and 16:9 at once, and there are exactly three ways out. Crop, which works when the subject occupies a small part of the frame and fails when the composition is the point. Pad with bars of background colour, which is honest and often right for a logo or a cut-out, and looks deliberate when the padding is a brand colour rather than default white. Or compose wide with a generous margin and crop each destination from the same source, which is what actually works when one asset has to appear in six places.
The third is a decision made before the photograph exists, not after, which is why it is the one people skip.
Tools that work with this
Related terms
- DPIDPI is the number of ink dots a printer places per inch, and in everyday use it is the ratio that converts an image's pixel dimensions into a physical printed size.
- Raster vs vectorA raster image stores a fixed grid of pixels and degrades when enlarged; a vector image stores shapes as mathematical descriptions and renders sharply at any size.
- Bicubic interpolationBicubic interpolation is a resampling method that estimates each new pixel from a weighted cubic function of the sixteen surrounding source pixels, producing smoother results than simpler methods without adding any real detail.
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