Width and height describe how many pixels an image contains. File size describes how many bytes are needed to store it. They are related, but they are not the same measurement.
Dimensions describe the pixel grid
An image that is 1200 × 800 contains 960,000 pixels. Doubling both dimensions to 2400 × 1600 creates four times as many pixels, not twice as many. That larger grid usually requires more storage and more work for the browser to decode.
Aspect ratio is the relationship between width and height. Resizing from 1200 × 800 to 600 × 400 preserves the 3:2 ratio. Resizing to 600 × 600 either stretches the image, crops it or adds empty space depending on the selected fit mode.
File size depends on more than pixel count
A smooth studio background compresses more efficiently than grass, hair, confetti or digital noise because repeated visual patterns are easier to represent. Format, quality setting, metadata and transparency also affect the final number of bytes.
This is why two 1200 × 800 JPEG files can differ greatly in size. One may contain a simple illustration while the other contains a detailed night photograph.
DPI usually does not change web display size
DPI or PPI metadata is mainly relevant to physical print dimensions. On a website, browsers generally display images according to CSS pixels and the actual pixel dimensions of the file. Changing a 72-DPI label to 300 DPI without resampling does not create additional detail.
Which setting should you change?
- Change dimensions when the image contains far more pixels than the final use requires.
- Change quality when dimensions are appropriate but the encoded file is still too large.
- Change format when the current format is inefficient for the type of content.
- Crop when unnecessary background consumes pixels and storage.
This guide was reviewed for practical clarity and updated for the current NEXDOWNLOAD toolset on July 28, 2026.