One target format per batch
Decide the destination format before selecting files and convert the whole batch to it. Mixed-target batches defeat the purpose: you lose the ability to compare results and you will re-run half the files anyway.
The most common batch conversions have obvious targets: website images → WebP, client deliverables → JPG, archival graphics → PNG. Name the batch's purpose, and the format usually picks itself.
Tame mixed sources first
Batches often mix sources — some PNG screenshots, some JPG photos, a WebP or two. That is fine, but know what each brings: PNGs with transparency need a transparency-capable target (PNG or WebP), or the transparent areas flatten to solid color.
Quick pre-sort saves trouble: pull transparency-needing images into their own batch targeting PNG or WebP, and convert the rest to whatever the job needs. Two clean batches beat one confused one.
Watch quality on lossy targets
When the target is JPG or WebP, the quality slider applies to the whole batch at once — and re-converts everything live when you move it. Find one setting that satisfies the most demanding image in the batch; the rest will be fine.
Beware converting already-lossy JPGs to WebP at low quality: you are re-compressing compressed pixels. Start from the highest-quality sources available, and keep the target quality at 75+ unless the images are thumbnails.
Verify and organize the output
Before downloading, scan the cards: every file converted, sizes look sane, transparency intact where needed. The before/after sizes are your early warning — a converted file larger than its source deserves a second look at your format choice.
Download the ZIP into a clearly labeled folder and replace the old files at their destination promptly. Converted images have a way of lingering in downloads folders while the website keeps serving the old ones.
After the batch: replacement discipline
A converted batch only pays off when the new files replace the old ones everywhere they live. Work through replacement systematically: website media libraries, document embeds, shared drives. The classic failure is converting perfectly and then forgetting — the old files keep serving while the new ones gather dust in a downloads folder.
Keep a conversion log for large projects: source folder, target format, quality setting, date. When new images arrive next month, the log turns a fresh project into a repeatable routine. Future you — or whoever inherits the task — follows the same proven recipe instead of reinventing it. A log also settles debates: when someone asks why the site uses WebP, the documented decision answers in seconds.
Frequently asked questions
Can I convert different formats in one batch?
Yes — sources can mix freely (PNG, JPG, WebP together). Just pick one target format for the batch and watch out for transparency when targeting JPG.
What if some images need transparency?
Convert those to PNG or WebP, which support transparency. Pull them into a separate batch rather than mixing with images headed for JPG.
Does batch conversion lower quality?
Only if the target is lossy (JPG/WebP) — then the quality slider governs the trade-off. Converting to PNG is lossless and pixel-exact.
Why is my converted file bigger than the original?
Usually a format mismatch for the content — e.g., a photo converted to PNG. Switch photographic content to JPG or WebP for dramatically smaller files.