How to batch resize hundreds of images for free

Resizing one photo is a minor chore. Resizing four hundred, one at a time, is how an afternoon disappears, and it is completely unnecessary, because every platform has had a free batch tool for years.

The tools are easy. The part that catches people out is the setup around them: where the output goes, what the files are called, and whether the originals are still there afterwards.

Choosing a tool

Everything above except the last row keeps your files on your own machine. For product photos, client work or anything unreleased, that is not a minor detail.

The method, whichever tool you use

Step 1: Copy the originals somewhere safe first

Duplicate the folder before you touch it. This is the cheapest insurance in imaging. If the batch goes wrong (wrong size, wrong format, wrong folder), you lose two minutes instead of a shoot.

Step 2: Decide the target size and ratio

Pick the largest size any destination needs, and crop to shape first if the shape is changing. Batch tools resize; most of them do not compose. If the images need to become square, crop them to square before the resize pass.

Step 3: Run the job on five files as a test

Never run an untested job on the whole folder. Process five, open them, check the dimensions and look at one at 100%. Almost every batch disaster would have been caught by this step.

Step 4: Run the full batch into a clean output folder

Point the output at an empty folder named for the job, such as resized-2000px rather than new folder. When you come back in three months, the name is the only documentation you will have.

Step 5: Compress afterwards, as a second pass

Resize and compress are separate operations. Resize the folder, then run the output through a compressor at quality 80. Doing both in one badly configured pass is how people end up with 400 images at quality 30.

Watch out for the overwrite option. Several batch tools offer “replace originals” as a convenience, and it is the single most destructive checkbox in image editing. There is no recycle bin for a file that was rewritten in place. The original bytes are simply gone.

Windows, step by step

1. Install PowerToys from the Microsoft Store. It is free and made by Microsoft.
2. Enable Image Resizer in the PowerToys settings if it is not already on.
3. Select your files in Explorer, right-click, and choose Resize pictures.
4. Pick a preset or enter custom dimensions, and confirm that “Make pictures smaller but not larger” is ticked if you do not want small files enlarged.
5. Leave “Resize the original pictures” unticked. PowerToys then saves copies named by the File name format in its settings. For example, the format %1 (%2) turns example.png into example (Small).png.

For a scripted alternative with no install, PowerShell can do the same job using the built-in .NET imaging classes, though it is considerably more typing than the right-click menu.

macOS, step by step

1. Select the files in Finder, Control-click, choose Quick Actions, then Convert Image (click More if it is not listed).
2. Choose the format and the image size: Small, Medium, Large or Actual Size. Converted copies appear alongside the originals.
3. For exact pixel values, open the files in Preview instead, press Command-A to select all in the sidebar, then Tools → Adjust Size.
4. Tick “Scale proportionally” and enter the width. Every selected image is resized at once.
5. Use File → Export Selected Images to write them to a new folder rather than saving over the originals.

ImageMagick, for when there are thousands

The -path out/ flag is what protects your originals. Without it, mogrify edits files in place, which is exactly the behaviour the warning above is about. Create the out folder before you run anything.

The short version

Copy, test on five, then run the whole folder into a clean output directory. That sequence turns an afternoon of clicking into about four minutes, on any operating system, for free.

Get the dimensions right first with resizing without distorting, settle the shape with aspect ratios explained, and finish the job with compression that does not cost quality.