A file described as a 300 DPI export is not automatically too large for a website. Before changing it, inspect its pixel width and height. A print-resolution tag, the number of image pixels and the size of the image on the page describe different things.
This guide uses an 1800 by 1200 pixel JPEG tagged at 300 pixels per inch, then prepares a 900 by 600 web candidate with the Image Resizer. The target dimensions are an example requirement, not a standard for every website.
Separate pixels, print resolution and page size
| Measurement | Example | What it describes |
|---|---|---|
| Pixel dimensions | 1800 by 1200 pixels | The width and height of the image grid. |
| Print resolution | 300 pixels per inch | How densely those pixels map to a physical print. |
| Displayed page size | 900 by 600 CSS pixels | The space the web layout gives the image. |
Image resolution is more precisely called PPI, for pixels per inch. DPI describes printer dots, although file properties and export instructions sometimes use that label for image resolution. The GIMP Print Size documentation distinguishes the two and explains that changing print size without resampling leaves the pixel count unchanged.
Calculate what the print tag means
For the source in this example:
1800 pixels ÷ 300 pixels per inch = 6 inches
1200 pixels ÷ 300 pixels per inch = 4 inchesChanging only the print resolution to 150 PPI, without resampling, would describe a 12 by 8 inch print. The file would still contain an 1800 by 1200 image. That change does not create a 900-pixel-wide web version.
In a controlled check, two JPEG fixtures shared the same decoded 1800 by 1200 pixels but carried different resolution metadata: 300 PPI and 72 PPI. In the test browser, the tool reported 1800 x 1200 for both. The print-resolution value alone did not determine their reported dimensions.
Changing resolution with resampling enabled in an editor can change pixel dimensions. Check the resulting width and height rather than assuming every resolution change is metadata-only.
Export the required pixel dimensions
Keep the original print export separately. For the 1800 by 1200 source, use this procedure:
- Open the Image Resizer and select the JPEG. Confirm that it reports 1800 x 1200 as the original size.
- Under Resize by, choose Pixel dimensions.
- Keep Maintain aspect ratio checked.
- Set Width (px) to 900. The height should update to 600.
- Choose JPEG (.jpg) and set Quality to 85 for this comparison.
- Select Resize image, check the reported new size, then select Download result.
The quality setting is a starting point for inspecting this candidate, not a required web setting. The operation reduces 2,160,000 image pixels to 540,000: half the width and height, and one quarter of the pixel count. It creates a resampled image rather than merely editing a print tag.
Set the page size separately
The export does not set the width of an image block in your website theme. A 900 by 600 resource can be displayed at 900 by 600 CSS pixels or at a smaller size, such as 450 by 300. The image element and CSS control that placement; the MDN image width reference documents dimensions in CSS pixels.
If you need multiple resources for different display densities, follow the guide to preparing a 2x image. Do not substitute a 72 PPI metadata change for choosing suitable pixel dimensions and page markup.
Verify the download without chasing its DPI label
Open the downloaded file and confirm 900 by 600 pixel dimensions. Inspect fine lettering and edges at the intended page size, then compare the actual byte size. A quarter of the pixels does not promise a quarter of the file size.
The resizer has no control for setting a requested PPI value. It creates a new file through browser canvas, as described in the MDN canvas export documentation. Keep the print master and check downloaded metadata separately if print settings matter. A resolution tag alone does not establish whether the web image has enough pixels or looks clear.