How to calculate image aspect ratio
Divide image width and height by their greatest common divisor. For 1200 × 800 pixels, that divisor is 400, so the source ratio is 3:2. A ratio describes shape, not resolution: 600 × 400 has the same shape with fewer pixels.
Crop to fill, or fit with padding?
A 16:9 crop inside a 1200 × 800 image keeps the full 1200-pixel width and 675 pixels of height. It removes 125 pixels of height in total, or 15.625% of the original area. The centered illustration shows the retained area in teal; check your subject and any text before cropping in an editor.
To keep every source pixel instead, place that image on a 1423 × 800 canvas. The added horizontal space preserves the image without stretching or upscaling it. Padding is additional canvas, not recovered image content. Both drawings are geometric examples, not image previews.
Understand the pixel boundary
Crop dimensions round down so they stay inside the source. Canvas dimensions round up so they contain it. Whole-pixel results can differ slightly from the exact target ratio: 1422.222… pixels becomes 1423. Use the target ratio in your editor when exact shape matters. Very narrow crops below one pixel cannot be represented and return an error.
Use a custom ratio supplied by your own brief. This calculator does not recommend platform placements, check file formats or file sizes, or guarantee that a social network will accept an asset. It does not upload or modify images.
Prepare the asset, then plan the post
Use the free content calendar planner to organize ideas and asset notes. PostifyNow provides workspace drafts, revision approval and per-target delivery records. This calculator does not connect accounts or publish posts; live publishing needs separately configured and authorized connections.