Converting images one at a time is fine for occasional tasks. When you're dealing with dozens or hundreds — a product catalogue, a photo archive, a set of assets for a web project — doing them individually isn't a workflow, it's just repetitive clicking. Batch conversion handles the whole set in one operation, with consistent output settings across every file.
The right tool depends on your volume, how often you do it, and how much control you need over the output. Here's a practical breakdown.
Browser-based tools
Portimg handles batch image conversion in the browser without any installation. Upload multiple files, select your output format — JPG, PNG, WebP, AVIF — and download the results as a ZIP. No account required, and files are deleted from the server after processing. It's the fastest option for straightforward format conversion on a batch of files you have on hand right now.
The limitation of browser-based tools generally is that they're less suited to recurring tasks you do regularly. If you're converting new product images every week as part of a standing workflow, you'll eventually want something you can run without the manual upload-select-download cycle each time.
Desktop tools for higher volume
XnConvert is a free desktop application for Windows, Mac, and Linux that handles batch conversion across 500+ formats with more granular control than browser tools — resize, rotate, crop, adjust colour, apply filters, rename output files with custom naming patterns, all in a single batch operation. It's well suited for photographers and designers who process large volumes of images regularly and need more than just format conversion.
IrfanView (Windows) is a lightweight image viewer with capable batch processing built in. It's been around long enough to be reliable and is faster to run than heavier applications. If you're on Windows and processing large batches frequently, it's worth having installed.
Preview with Automator (Mac) lets you build repeatable batch workflows using macOS's built-in automation tools. If you do the same conversion task regularly — resizing images to a standard dimension for a particular use, or converting a folder of screenshots to JPG — an Automator workflow runs it in one click without opening any application manually.
ImageMagick is a command-line tool available on all platforms that handles virtually any image operation in batch via scripting. It's the most powerful option but requires comfort with the terminal. A simple ImageMagick command can convert an entire folder of PNGs to WebP at a specified quality level in seconds. If you're comfortable with basic command-line use, it's worth learning the core convert commands — the time investment pays back quickly on high-volume tasks.
Getting consistent results
A few habits that make batch conversion less likely to produce unexpected results:
Name files before processing. Descriptive, consistently-formatted file names make output easier to manage. Numbered sequences (01.jpg, 02.jpg) are useful when order matters. Random camera-generated names (IMG_4823.jpg) are harder to sort and identify later.
Test on a small sample first. Before running a batch of 500 images through any settings, convert five and check the output. File size, quality, colour accuracy, and dimension handling can all produce surprises until you've confirmed the settings work for your specific source material.
Keep originals until you've confirmed the output. Batch operations are hard to undo. If you're converting in place rather than to a separate output folder, keep a backup until you've verified the results are what you needed. Regenerating a batch from originals is straightforward; recovering from a lossy conversion that overwrote originals is not.
Format choice at scale
For web use, converting a folder of PNGs or JPGs to WebP before upload is one of the more impactful quick wins for page performance — WebP consistently produces smaller files at comparable visual quality, which reduces load times without any change to the images themselves. AVIF achieves even better compression but has narrower software support, so WebP is the safer default for most web workflows. For anything going to print or into professional design software, PNG or high-quality JPG remains the more compatible choice.