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How to Batch Convert 100+ Images at Once (Free)

Converting images one by one is miserable. Batch convert entire folders — format, size, quality — in one pass, without installing anything.

By Formatly

Sooner or later everyone faces the folder problem: 200 product photos in the wrong format, a wedding shoot that needs resizing, a decade of PNG screenshots eating disk space. Converting them one at a time is not a workflow — it’s a punishment. Here’s how to do the whole batch in one pass.

The golden rules of batch conversion

1. Never overwrite your originals. Convert into a new folder. Disk space is cheap; the original shoot, the client’s source files, or the only copy of a scanned archive is not. Name it clearly: photos-web/, converted-2026/, anything unambiguous.

2. One setting for the whole batch. Pick your format, quality, and dimensions once, apply to everything. Consistent settings mean consistent color, sharpness, and file sizes — which matters enormously for catalogs, galleries, and documentation.

3. Convert from the best source. Batch-converting JPGs that were already compressed is polishing a photocopy. If you have RAW, PNG, or TIFF originals, batch from those.

4. Spot-check before committing. Convert 3–5 representative images first (a dark one, a detailed one, one with text), inspect them at 100% zoom, then run the full batch with the confirmed settings.

What to batch together (and what to split)

Batch conversion works best on uniform sets: all photos, all screenshots, all product shots on the same background. Split the job when the content differs:

  • Photos vs. graphics — different ideal formats (JPG/WebP vs. PNG) and quality settings
  • Images with transparency — converting PNG→JPG kills transparency; handle these separately or keep them PNG
  • Mixed orientations — fine for format conversion, but resize batches should be split by orientation if you’re targeting exact dimensions

A quick sort before you start saves painful re-dos after.

Common batch jobs and the right settings

Folder of HEIC iPhone photos → JPG for sharing. Convert to JPG quality 90, keep original resolution. iPhone HEICs are typically 12–48 MP — plenty for any screen use.

Product catalog → web-ready WebP. Resize to your site’s max display width (often 1200–1600px), convert to WebP quality 80. This single batch often cuts a catalog from gigabytes to a few hundred megabytes.

PNG screenshots → JPG for documentation. Screenshots with photographic content convert beautifully; screenshots of pure UI/text should stay PNG or go WebP lossless. Split them.

TIFF scans → JPG for the web. Scans are huge; JPG quality 85–90 at a sensible resolution (2000px on the long edge is plenty for screen viewing).

Mixed camera RAWs → JPG proofs. If you only have JPGs already, don’t “convert” JPG→JPG at lower quality for proofs — use compression instead, which is the same operation done honestly.

How long does it take?

In-browser batch conversion processes roughly 1–3 images per second for typical photos on a modern laptop — a 200-image folder takes a few minutes. HEIC decoding and AVIF encoding are slower (that’s the codec, not the tool). The bottleneck is almost always your inspection time, not the conversion: the spot-check matters more than the processing speed.

Filenames and organization

Decide the naming scheme before you start:

  • Keep original names, change folder: originals/IMG_2041.heic → web/IMG_2041.jpg — simplest, preserves traceability
  • Add a suffix: IMG_2041-web.jpg — useful when originals and conversions live side by side
  • Sequential for galleries: product-001.jpg, product-002.jpg — only if the originals were already in the right order

Whatever you choose, be consistent. Future-you will thank present-you.

The privacy angle nobody mentions

Batch uploads are where “free online converters” get sketchy: you’re handing a stranger’s server your entire photo library — client work, unreleased products, personal photos — in one drag-and-drop. Server-side batch tools must receive all your files to process them. Client-side batch tools never do. For bulk jobs especially, the architecture matters more than the privacy policy.

Practical next steps