The Amazon Minimum Product Image size (1000×1000px)
Not every listing needs a giant file, and 1000x1000 is the practical floor for a usable Amazon product image. Amazon's absolute technical minimum is 500 pixels on the longest side, but images that small look soft and, crucially, do not qualify for hover-to-zoom. At 1000x1000 your photo displays cleanly on the product page and thumbnails while keeping the file lightweight, which is handy when you are uploading many SKUs or working with limited source resolution.
The square 1:1 ratio is the same requirement as the higher-resolution main image, because Amazon frames all catalog images as squares. Choosing exactly 1000x1000 means the product is centered and consistent everywhere it appears, from search results to the mobile app. If your source photo is only large enough to reach roughly 1000px cleanly, resizing to this size is a sensible middle ground: it satisfies catalog rules without upscaling a small original into a blurry mess.
Keep in mind the trade-off. A 1000px image meets the rules but misses the zoom experience that a 1600px-plus image unlocks, so for hero products you will usually want the larger 2000x2000 version instead. Use 1000x1000 for secondary photos, variation swatches, or catalog entries where zoom is not critical. Amazon's requirements differ by category and change periodically, and everything here resizes 100% in your browser with no upload and for free, so verify the current minimum for your category before publishing.