How to Change Image Resolution in GIMP

A lot of people open GIMP to "change the resolution" and end up accidentally making their image smaller or blurry. Resolution and image size are related, but they are not the same thing - and GIMP handles them separately. This guide clears up the confusion and walks you through every scenario.

Resolution vs. Image Size - The Difference

Resolution (measured in DPI - dots per inch, or PPI - pixels per inch) tells a printer how many pixels to squeeze into each inch of paper. It does not change the pixel dimensions of the image file itself.

Image size (width and height in pixels) is the actual number of pixels in the file. That is what changes when you scale the image.

On screen, DPI makes no visible difference - a 72 DPI file and a 300 DPI file with the same pixel dimensions look identical on a monitor. DPI only matters when printing.

How to Change DPI/PPI in GIMP

To change just the resolution metadata without touching the pixels:

1. Go to Image > Print Size.
2. You will see fields for X resolution and Y resolution (in pixels/in or pixels/mm).
3. Type your new DPI value in the X resolution field. The Y value will update automatically if they are linked.
4. Click OK.

After clicking OK, the pixel dimensions stay exactly the same. Only the embedded metadata changes. This will not make a low-res photo sharper - to get more pixels, you need to scale up (which adds interpolated pixels, not real detail).

Setting Resolution for Print

Standard print resolutions:

• 300 DPI - professional print quality (photos, brochures, business cards)
• 150 DPI - acceptable for large-format prints viewed from a distance
• 72 DPI - screen only, not suitable for print

For a 4x6 inch photo print at 300 DPI, you need at least 1200x1800 pixels. If your image is smaller than that, set the DPI lower or scale the image up and accept some softness.

The Scale Image tool at Image > Scale Image is where you increase pixel dimensions if needed. Just be aware that GIMP is adding new pixels by guessing (interpolation) - it cannot create detail that was not there.

Resolution for Web and Screens

Web images are measured in pixels, not inches. Resolution metadata is ignored by browsers. For web:

• Focus on pixel dimensions, not DPI
• A full-width hero image is usually 1920px wide
• A blog image is typically 1200px wide
• DPI can be left at 72 or 96 - it will not affect how it looks online

What does affect web performance is file size. Use File > Export As and choose JPEG or WebP with compression to keep file sizes small. A 1200px-wide JPEG at 80% quality is usually under 200KB.

Scaling the Image at the Same Time

If you want to change both DPI and pixel size together (for example, converting a 72 DPI web image to a 300 DPI print image with proportionally more pixels):

1. Go to Image > Scale Image.
2. Change the resolution field to 300.
3. GIMP will automatically recalculate the pixel dimensions to match the physical size at the new resolution.
4. Choose an interpolation method - Cubic or Sinc (Lanczos3) gives the best quality for upscaling.
5. Click Scale.

This changes both the metadata and the actual pixel count. The image will be larger in file size and pixel dimensions, but the added pixels are interpolated - the underlying image quality does not improve beyond what the original captured.