Image File ToolsFile size and dimensions. What’s the difference?
Dimensions describe how many pixels an image contains. File size describes how many bytes it takes to store those pixels. Upload forms can set a limit on either—or both.
Pixels measure the canvas
A 1200 × 800 image contains 960,000 pixels. Resize it to 600 × 400 and it contains a quarter as many pixels. The shape stays the same, but less detail is available when you enlarge it or print it.
Kilobytes measure the file
Two images with identical dimensions can have very different file sizes. A detailed photograph is harder to compress than a plain background. Format, encoding quality and metadata also affect the number of bytes.
| A form asks for… | Adjust… | Check before downloading |
|---|---|---|
| Under 200 KB | Compression and, if needed, dimensions | Actual output bytes |
| 600 × 400 pixels | Width and height | The resulting aspect ratio |
| 600 × 400 and under 200 KB | Dimensions, then compression | Both requirements |
Fit both requirements in one step
In the compressor, open “Also set pixel dimensions.” Enter the form’s width and height and your maximum KB limit. Keep “Allow smaller dimensions if needed” off when a form requires exact dimensions. An impossible limit will be reported rather than silently breaking your requirements.
With the aspect ratio locked, the image fits inside the dimension box without stretching. That may produce dimensions smaller than the box. We do not crop or certify passport photos.
How Image File Tools counts a KB
We use decimal units: 1 KB = 1,000 bytes and 1 MB = 1,000,000 bytes. A 200 KB target means at most 200,000 bytes. That also fits a 200 KiB limit (204,800 bytes), but a site may have other rules for format or dimensions.
Have the dimensions right, but the file is still too large?
Make it fit