How to Batch Convert Images Offline
Convert a folder of images on your own computer, keep the originals safe and check the results before deleting anything.
Batch conversion should save time, not leave you with 400 mystery files and no idea where the originals went. The easy way is to keep the source folder untouched and put every converted file in a new folder.
You can then drag the whole batch into How to Convert, choose one output format and click Convert. The only extra work worth doing is a small test before you run a large or important folder.
Before you convert the whole folder
Put similar images together. Photos usually belong in JPG, WebP or AVIF. Screenshots and transparent graphics usually belong in PNG or WebP. If you mix all of those in one batch and force them into JPG, any transparent areas will need a solid background.
Make a copy of anything irreplaceable. How to Convert creates new files, but a separate source folder still makes the job much easier to check and undo.
The simple offline batch workflow
Create an output folder
Name it after the result you want, such as Website images - WebP. Leave the source folder alone.
Test a few different images
Choose one photo, one screenshot and one image with transparency if your folder contains them. Convert those first and open the results.
Add the full batch
Drag the remaining files into How to Convert. Select the output format once, then click Convert.
Save and compare the file count
Save everything into the output folder. The number of new files should match the number you added, unless the app clearly reports a file it could not convert.
Common problems
Some converted files are missing
One or more source formats were not supported or two outputs ended up with the same name.
Read the result shown for each file and compare the source and output counts before deleting or moving anything.
Transparent areas have a white or black box
JPG does not support transparency.
Use PNG or WebP, or deliberately choose the background colour you want.
Small text looks blurry
The batch setting was chosen for photos.
Put screenshots and graphics in a separate batch and use PNG or a higher-quality setting.
Frequently asked questions
Can I convert a whole folder at once?
Yes. Select the files in the folder and drag them into the desktop app. You choose the output once for the batch.
Why convert offline?
It avoids waiting for uploads and keeps private, client or work images on your computer.
Should the converted files go beside the originals?
A separate output folder is easier to check and much safer.
What should I test first?
Include the largest image and anything unusual, especially transparency, small text or a very different file type.
Extra: When one batch should really be two
Split photos from logos, screenshots and illustrations. A setting that looks great on a photo can make small text fuzzy, while a setting that keeps text perfectly sharp can make every photo unnecessarily large.
Also separate animated images if you need the animation. Some output formats only keep a single frame, which is easy to miss when you are looking at a folder of thumbnails.
