How do I resize an image in ImageMagick without losing the aspect ratio?

Pass a plain WxH box with no suffix, for example -resize 800x600. ImageMagick fits the image inside that box and preserves the ratio. Adding an exclamation mark forces the exact size and distorts the image.

What is the difference between -resize and -thumbnail?

-thumbnail is -resize plus -strip, with a fast pre-scale step. It is quicker and produces smaller files, but it discards EXIF data and ICC colour profiles, which can shift colours on wide-gamut images.

How do I resize an image only if it is larger than a certain size?

Append a greater-than sign to the geometry and quote it: -resize '1600x1600>'. Images already smaller are copied through unchanged. The quotes are required or the shell treats the character as redirection.

How do I make a square thumbnail without stretching the image?

Scale to cover the box with the caret suffix, then crop the overflow: -resize '400x400^' -gravity center -extent 400x400.

ImageMagick resize command generator

Build the exact ImageMagick resize command. Explains ^ ! > < and % suffixes, keeps aspect ratio, makes exact-size thumbnails without distortion. IM7 and IM6 syntax.

Resizing is the first thing almost everyone uses ImageMagick for, and it is also where the most time gets lost — because -resize behaves completely differently depending on a single character you put after the size.

Set your options in the builder above and copy the command. The rest of this page explains what it is doing, so the next time you can write it yourself.

The five resize behaviours

Command	What you get
`-resize 800x600`	Fits inside 800×600. Aspect ratio kept, so one side ends up smaller than asked.
`-resize 800x600!`	Forces exactly 800×600 and squashes the image if the ratio differs.
`-resize '800x600^'`	Fills the box, overflowing on one axis. Pair with `-extent` to crop the overflow.
`-resize '800x600>'`	Shrinks only if the image is larger. Smaller images pass through untouched.
`-resize '800x600<'`	Enlarges only if the image is smaller.

Resize without distorting the image

Give -resize a plain WxH box and ImageMagick will never distort — it fits the image inside and preserves the aspect ratio. Distortion only happens when you add !.

magick input.jpg -resize 1200x1200 output.jpg

Resize to a width and let the height follow

magick input.jpg -resize 800 output.jpg       # width 800
magick input.jpg -resize x600 output.jpg      # height 600

That leading x is the single most common ImageMagick mistake. -resize 600 is a width; only -resize x600 is a height.

Exact-size thumbnails with no distortion

This is the recipe you actually want for avatars, product grids and card images — scale to cover the box, then trim the overflow from the centre:

magick input.jpg -resize '400x400^' -gravity center -extent 400x400 output.jpg

A bare -crop fails here, because images smaller than 400×400 would not fill the frame. The ^ guarantees full coverage first.

Only shrink large images, never upscale small ones

The standard safe transform for anything users upload:

magick input.jpg -resize '1600x1600>' -quality 85 output.jpg

The > must be quoted. Unquoted, your shell reads it as output redirection, silently drops it, and creates an empty file named 1600.

Which resize operator should you use?

-resize — filtered, high quality resampling. The default answer.
-thumbnail — a fast pre-scale then resize, plus an automatic -strip. Fastest for galleries, but it drops ICC colour profiles as well as EXIF.
-scale — simple pixel averaging with no filter. Use for pixel art and for pixelation effects.
-sample — pure nearest neighbour. Picks pixels, never blends.

Sharpening after a downscale

Every downscale softens edges. A conservative unsharp mask restores them without producing halos:

magick input.jpg -resize 1200 -unsharp 0x0.75+0.75+0.008 output.jpg

Resize every image in a folder

mkdir -p out
for f in *.jpg; do
  magick "$f" -resize '1600x1600>' -quality 85 "out/${f%.*}.jpg"
done

mogrify -resize '1600x1600>' *.jpg does the same in one line but overwrites your originals in place. If you use it, always add -path out. Tick “Batch mode” in the builder above to get the loop for your shell.