An image has two different sizes. Pixel dimensions describe its width and height. File size describes how much storage the encoded file takes. One does not tell you the other.
Start with the destination’s dimensions.
If a website asks for a 1600 px longest edge, set that value rather than guessing a megabyte target. A landscape photo will use 1600 for its width; a portrait photo will use it for its height. Preserving the ratio keeps circles round and faces in proportion.
Example: 2400 × 1600 pixels has a 3:2 ratio. At a 1200 px longest edge, it becomes 1200 × 800. The result has one quarter as many pixels, because both edges are halved.
Why file sizes still vary.
Two 1200 × 800 images can have very different byte counts. A smooth background is easier to encode than dense texture. Format, transparency and compression settings also matter. You cannot promise a fixed file size from dimensions alone.
For a photograph, JPEG quality is often the next setting to adjust. Export once, inspect details such as hair and lettering, and reduce quality only as far as the destination needs. PNG is lossless and often larger for photographs; shrinking dimensions may reduce its size, but choosing a JPEG quality slider has no effect on a PNG export.
No upscale means no invented detail.
If your source is smaller than the chosen longest edge, Pixel Zoodle keeps it at the original size. Enlarging an image would create extra pixels by interpolation, which does not recover missing detail. Find a larger original if the destination needs one.
A practical order of operations.
- Keep a copy of the original, especially before cropping or re-exporting a JPEG.
- Check the destination’s dimensions, accepted format and maximum file size.
- Resize once to the needed dimensions.
- Choose a format and, for JPEG, a quality setting.
- Open the exported file. Check fine detail and confirm its byte size before submitting.