Images tower · floor

How to resize an image in GIMP, and the two traps after it

Learning how to resize an image in GIMP takes about a minute. The reason people search for it more than once is that two things go wrong afterwards, and neither is on the tutorial page that answers the question.

The steps first, from the manual rather than from memory.

The four steps, from GIMP’s own documentation

GIMP 3.2 user manual, read 21 August 2026. Four steps, and two of them are checks rather than actions.

  1. Ignore the zoom level “GIMP sets the zoom so that it displays nicely on the screen… This does not change the actual image.” The percentage in the status bar is how you are looking at it, not what it is.
  2. Check the mode in the title bar “If the mode shows as RGB in the title bar, you are fine. If the mode says Indexed or Grayscale”, that is a different job first.
  3. Image → Scale Image… Also reachable by right-clicking the image. Enter the width you want; “when you change one of the image’s dimensions, GIMP changes the other dimension proportionally”, so the picture does not stretch.
  4. Work in pixels, and ignore resolution See the box below — this is the step where most people go wrong.

First trap: the resolution box does nothing for a screen

The Scale Image dialog has two sections, and the second one is a trap for anyone resizing a photo to email or post. GIMP’s manual is unambiguous: “Resolution applies to printing only and has no effect on the image’s size when it is displayed on a monitor or a mobile device.”

The reason it gives is the correct one: different devices have different pixel sizes, so an image that is a certain physical size on a phone “might display on other devices… in another size altogether”. Hence the instruction: “For the purpose of displaying an image on a screen, you can ignore the resolution parameter. For the same reason, do not use any size unit other than the pixel in the height / width fields.”

If you do not know what number to type, the manual gives a range: “common screen sizes range between 600 pixels for simpler phones and 1920 pixels for an HD screen”.

That single paragraph settles an argument people have with themselves for years. Resizing a photo for a website, an email or a message has nothing to do with DPI. The only number that matters is the pixel width, and the resolution field is there for the other job — printing — which is covered on a different page of the same manual.

Second trap: saving does not give you a JPEG

This is the step the tutorial page stops before, and it is where people conclude that GIMP is broken. “Images are loaded and saved as .XCF files. Your JPG image has been loaded as XCF.” File → Save produces GIMP’s own working format, which almost nothing else opens.

To get a normal picture file back out, the manual names two routes: File → Overwrite image-name.jpg, which replaces the original, or File → Export As, which opens the Export Image dialog and lets you choose a new name and format.

And one warning worth carrying beyond GIMP entirely: “repeated saving in the JPG format causes more and more image degradation.” Every round trip through JPEG costs quality, so open the original each time rather than re-editing your own exports.

Why GIMP works this way, since it looks like an inconvenience. Its own format keeps everything a picture file cannot: layers, selections, undo history, transparency handled its way. Saving to JPEG would silently throw that away, so the program refuses to blur the distinction — you save your work, and you export a picture. Once you know that, the behaviour stops being a fault and becomes a reasonable position, and it is the same one several other editors take.

Making the file smaller, which is usually the real goal. Scaling and compressing are different levers and people reach for the wrong one. Scaling changes the dimensions — fewer pixels, so a smaller file, and the picture is physically smaller. Compression keeps the dimensions and lowers the quality setting in the Export dialog. The manual states the trade in one line: “the less space an image takes, the more detail from the original image you lose.” For sending a photo, scaling first and then exporting at a sensible quality does more than either alone.

Do you need GIMP for this at all? Honestly, often not. Resizing one image is built into the Photos app on Windows and Preview on a Mac, and neither requires a download. GIMP earns its place when you are doing this repeatedly, when you want precise control over the export, or when you want a full editor that costs nothing and has no subscription attached — which is the reason most people arrive at it.

What this floor does not do is compare GIMP against paid editors, because we have not run that test. What is here is the documented behaviour of one free program, quoted from its own manual with the version number and the date, so you can check every sentence against the source.

Where to start

Four ways in.

“I just need the steps.”
They are above — then read the two traps in the file afterwards
“My saved file will not open anywhere.”
That is the second trap — the file afterwards
“I only want a smaller file.”
Go to making it smaller
“Is there something simpler?”
See without installing anything

The file afterwards

What comes out of an editor is a separate question from what you did inside it, and it is where most of the confusion lives.

PNG or JPG?What each format is for, and which one you actually want at the end.Open this floor → HEIC filesWhy photos from an iPhone will not open on somebody else’s computer, and the three ways round it.Open this floor → WebP to JPGThe format the web moved to, and what to do when something will not accept it.Open this floor →

Making it smaller

Scaling and compressing are different levers with different costs, and reaching for the wrong one is the common mistake.

Resizing photos on iPhoneThe same job on a phone, where the tools and the limits are different.Open this floor → Compressing a PDFThe same trade in a different tower: what gets smaller, and what quality it costs.Open this floor → Compressing a video on iPhoneThere is no compress button, and for most reasons you do not need one.Open this floor →

Without installing anything

For a single image, the tools already on your machine are usually enough, and they do not send the file anywhere.

Word processors without the cloudWhat still works entirely on your own machine, and what it costs.Open this floor → Safe PDF convertersWhat an upload site keeps, and when it matters.Open this floor → Freeing up disk spaceThe nine methods Microsoft publishes in its own order.Open this floor →

Where images go wrong

Format, size, quality and metadata are four separate things, and most image problems are one of them wearing another’s clothes.

Large files by emailSending something too big to attach, without uploading it somewhere you have not read the terms of.Open this floor → Scanning documents with a phoneTurning paper into a file that is actually readable later.Open this floor →
What employers findWhat a search for your name returns, images included.Being built

What this tower will not do

It will not tell you to change the DPI to resize for a screen. The manual says resolution “applies to printing only”, and that sentence is quoted above because it settles the most common confusion in this subject.

It will not compare GIMP with paid editors. We have not run that test, and until we have, a verdict here would be an impression.

And it will not send you to an upload site to do something your own computer already does — which, for a single image, it does. What holds instead is simple: every step and every quotation on this page comes from the GIMP 3.2 user manual, with the date it was read.

Where this page got its facts

  1. GIMP 3.2 user manual — Change the Size of an Image for the screen, on zoom versus size, image mode, Scale Image, and why resolution applies to printing only — docs.gimp.org, read 21 August 2026.
  2. GIMP 3.2 user manual — Compressing Images, on saving as XCF, File → Overwrite and File → Export As, and the degradation caused by repeated JPEG saving — docs.gimp.org, read 21 August 2026.

Written by Alberto Gulotta

Founder and editor of AI Tools Primer, writing from Palermo, Italy. Thirty-five years of taking computers apart, starting with a Commodore 64 — the long version is on the about page.

Something wrong on this page? Write to aitoolsprimer@gmail.com and it gets fixed.

Written on 21 August 2026.

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