What a 1920 by 1080 still is for
Full HD, sixteen by nine
1920 across and 1080 down is the still people mean when they say Full HD or 1080p. The shape is 16:9. Conference-room displays, many slide decks, and a 1080p video timeline are built around that rectangle. A photograph that is 4:3 or square will not fill it without a crop or a stretch, so decide which you accept before you export. This page is for the moment a brief says Full HD, 1080p, or a widescreen banner, and you need the file to report those pixels.
A video frame beside a smaller thumbnail
A 1080p video frame is this size. A YouTube thumbnail in the social presets is 1280 by 720, which is the same shape and a smaller file. Use 1920 by 1080 when the still will sit on a 1080p timeline, fill a slide, or act as a virtual background on a 1080p display. Use the smaller thumbnail when the only job is a clickable preview. Mixing them up makes either a heavy thumb or a soft frame that a player has to enlarge.
Type the pair, then look at the source
Type 1920 in the width field and 1080 in the height field. The resizer reads one image, the first file you add, and draws it to those pixels on this device. Each side may be as large as 10000, so this pair is well inside the limit. If the original is already wider than 1920, you are shrinking, and edges stay cleaner. If the original is a 640 pixel phone crop, the export gets bigger and softer. Enlarging does not invent detail. Go back to a larger master when faces look plastic.
Format after the box is right
JPG, PNG, WebP, and GIF can be the input. A kilobyte target applies only to JPEG and WebP. Leave that box empty and those two formats save at quality 0.92. PNG ignores the kilobyte target, which is the right choice for a flat title card you do not want squeezed by a size aim. When a learning system still rejects the JPEG for weight, run the image compressor after the pixels are correct. The geometry and the file weight are two different problems.