When to Convert Images: The Definitive Format Switching Guide
Not every image needs converting — and converting the wrong way can cost you quality without gaining anything. Here is a clear decision framework for every common scenario.
The six most common conversion scenarios
Scenario 1: JPG to WebP — almost always worth doing
When: Any time you're displaying photographs on a website in a modern browser.
Why: WebP delivers 25–35% smaller files at equivalent visual quality compared to JPG. On a typical content site with 40–50 images, that translates to several hundred kilobytes of saved page weight — enough to meaningfully improve LCP and overall page load time.
Caution: Email clients largely don't support WebP. For email marketing campaigns, stick with JPG. For the web, convert everything you can.
What you lose: Nothing of significance. If you need to edit the image later, keep the original JPG as your editing master and generate a fresh WebP for delivery each time.
Scenario 2: PNG to WebP — definitely do this
When: When serving logos, icons, graphics with transparency, or any PNG on a website.
Why: WebP lossless is roughly 26% smaller than PNG for the same image. WebP supports full alpha channel transparency. There's no quality loss — it's a lossless-to-lossless conversion.
Caution: For logos and icons, SVG is usually even better if the original is vector-based. SVG scales to any size with no quality loss at file sizes typically under 5KB. Reserve PNG/WebP for raster images that can't be represented as SVG.
Scenario 3: PNG to JPG — only for photos without transparency
When: When you have a PNG photograph that doesn't use transparency, and you need a smaller file for web delivery or email.
Why: JPEG's lossy compression is dramatically more efficient for photographic content. A 1.4MB PNG photograph often compresses to under 250KB as a JPG at 85% quality — a massive reduction with negligible visual impact at normal screen viewing sizes.
Never do this for: Screenshots, graphics with text, logos, or anything with sharp edges where JPG's compression artifacts will be visible. PNG and WebP lossless are the right formats for those.
Transparency warning: JPG doesn't support transparency. Any transparent areas in your PNG will become white in the JPG output. If you need transparency, convert to WebP instead.
Scenario 4: JPG to PNG — almost never useful
When: Rarely, if ever, for web delivery.
Why not: JPEG is a lossy format. Once data has been discarded during JPEG compression, converting to PNG (lossless) doesn't recover it — the data simply isn't there. All you get is a larger file with the same quality as the source JPEG. It's the image equivalent of saving a Word document as PDF and claiming you now have better quality text.
The one exception: If you need to do multiple rounds of editing and re-saving on a JPEG image, convert to PNG as your intermediate editing format to prevent compounding compression artifacts with each save. When editing is finished, compress and export as JPEG or WebP for delivery.
Scenario 5: WebP to JPG — for compatibility
When: When you need to share a WebP image with a tool, platform, or person that doesn't accept WebP — older desktop software, some CMS plugins, some third-party integrations.
Why: WebP support in consumer software and email clients still lags behind browser support. If someone tells you they can't open a WebP file, convert it to JPG.
Scenario 6: WebP to PNG — for editing or transparency
When: When you need to import a WebP image into design software that doesn't support WebP, or when you need to preserve transparency in a lossless format for editing.
The three golden rules of image conversion
- Always keep the original. Never overwrite your source file with a converted version. Keep originals in their native format (RAW, PNG, or highest-quality JPG) and generate converted files for each specific use case.
- Avoid lossy-to-lossy chains. Converting JPG to JPG (re-saving), or lossy WebP to lossy JPG, applies another round of compression on top of existing artifacts. Each generation loses more quality. The exception is conversion between different lossy formats at high quality settings, where the additional loss is minimal.
- Format for the destination, not the source. Ask "where will this image be displayed?" rather than "what format is it currently in?" The answer to the first question determines the right output format.
Quick reference table
| Situation | Convert to | Reason |
|---|---|---|
| Photo for website | WebP | 25–35% smaller than JPG, all modern browsers |
| Photo for email | JPG | Email clients don't support WebP |
| Logo for web (raster) | WebP or SVG | Smaller than PNG, supports transparency |
| Screenshot / UI | PNG or WebP lossless | Lossless needed for sharp text |
| Product photo (Amazon) | JPG | Amazon requires JPG for main images |
| Social media | JPG | Platforms recompress; start optimised |
| Editing master file | PNG or RAW | Lossless preserves quality through edit rounds |