Ship smaller images without uploading your assets
Resize to the size you display, convert to WebP or AVIF, and download a ZIP that keeps your file names. It all runs in your browser, so no image is ever uploaded.
Recommended settings
Settings for each kind of site image
Start from the linked preset and change only the settings listed. A resize value is the longest side: for several images, enter it as both Max width and Max height; for one, type it into its longer side.
| Image | Format | Goal | Resize | Start from |
|---|---|---|---|---|
| Hero and full-width imagesFills full-screen layouts on most laptops and desktops. | WebP | Quality 75 | 1920 px | Optimize images for your website |
| Content and in-article imagesAbout twice a typical content column, so they stay sharp on high-density screens. | WebP | Quality 75 | 1280 px | Optimize images for your website |
| Cards and thumbnailsTwice a 400 px card. Use twice the size your grid actually shows. | WebP | Quality 75 | 800 px | Optimize images for your website |
| AVIF versions for a <picture> elementUsually smaller than WebP at the same visual quality. Large photos take longer to encode. | AVIF | Quality 75 | Same as the WebP set | JPG to AVIF converter |
| Logos, icons and UI graphics with transparencyTransparency is kept. Keep vector logos as SVG: Graviton works on raster images. | WebP or PNG | Quality 80, or Lossless | Off | PNG to WebP converter |
| JPG fallbacksFor the <img> inside <picture>, and anywhere WebP isn’t accepted. | JPG | Quality 75 | Same as the WebP set | Compress JPEG images |
Hero and full-width images
Fills full-screen layouts on most laptops and desktops.
- Format
- WebP
- Goal
- Quality 75
- Resize
- 1920 px
Content and in-article images
About twice a typical content column, so they stay sharp on high-density screens.
- Format
- WebP
- Goal
- Quality 75
- Resize
- 1280 px
Cards and thumbnails
Twice a 400 px card. Use twice the size your grid actually shows.
- Format
- WebP
- Goal
- Quality 75
- Resize
- 800 px
AVIF versions for a <picture> element
Usually smaller than WebP at the same visual quality. Large photos take longer to encode.
- Format
- AVIF
- Goal
- Quality 75
- Resize
- Same as the WebP set
Logos, icons and UI graphics with transparency
Transparency is kept. Keep vector logos as SVG: Graviton works on raster images.
- Format
- WebP or PNG
- Goal
- Quality 80, or Lossless
- Resize
- Off
JPG fallbacks
For the <img> inside <picture>, and anywhere WebP isn’t accepted.
- Format
- JPG
- Goal
- Quality 75
- Resize
- Same as the WebP set
Every tool page is a preset, not a lock: change any setting and the rest stay as they are. Trying another format or quality is free, and downloading the same image again that day on the same device counts once.
Workflow
From source files to production in six steps
- 1
Tune on one image
Drop in one typical image and open the website preset: WebP, quality 75, 1920 px. Drag the before-and-after slider over text, edges and gradients. If you see banding or blur, raise quality to 80–85.
- 2
Set the size for each slot
Change Max width and Max height to where the image appears: 1920 for full-width, 1280 for content, 800 for thumbnails. Proportions are kept, and smaller images stay as they are.
- 3
Run the batch
Drop in up to 250 images at once, up to 100 MB each. JPG, PNG, WebP, AVIF, GIF and iPhone HEIC are all accepted.
- 4
Download the ZIP
Download them one by one or as a ZIP: 3 a day on Free, unlimited on Pro. Each file keeps its name with the new extension, so hero.jpg becomes hero.webp and updating references is a find-and-replace.
- 5
Make the AVIF set
Switch Format to AVIF and run the same images again. Compressing is unlimited, and downloading an image again the same day on the same device, in another format, counts once.
- 6
Serve with fallbacks
List the AVIF and WebP files as sources in a <picture> element with a compressed JPG as the fallback, and set width and height to prevent layout shift.
Why developers use it
Open-source encoders, no upload
Nothing leaves the page
Images are encoded in Web Workers with WebAssembly. Open your browser’s network tab while a batch runs: no image is uploaded.
Encoders you already trust
MozJPEG, libwebp, libavif and OxiPNG: the open-source encoders also used by Squoosh-style tools.
High-quality resizing
Downscaling uses high-quality resampling and keeps proportions; smaller images stay as they are unless you ask. A 4000 × 3000 photo set to 1920 becomes 1920 × 1440.
File names survive
Download files one by one or as a ZIP with the original names. Duplicates become “name (2).webp” instead of overwriting each other.
Clean output
Every image is saved without EXIF, GPS or camera metadata by default, and re-encoded images are converted to sRGB so colors match across browsers.
No upload wait
Work runs in parallel across your processor’s cores. Most photos take about a second; a 24-megapixel photo takes a couple of seconds.
FAQ
Questions from web developers
Should I serve WebP or AVIF?
Both, if your stack allows it. AVIF is usually smaller at the same visual quality, while WebP encodes faster and works in every modern browser. List AVIF first in a <picture> element with WebP and JPG fallbacks. If you can ship only one format, WebP is the safe default.
What width should I export at?
The largest width the image is shown at, times two for high-density screens. In practice: 1920 px for full-width images, 1280 px for content images and 800 px for thumbnails. Graviton leaves smaller sources at their size unless you turn on Enlarge smaller images.
Does Graviton have an API or a command-line tool?
No. Graviton is a browser tool. For images processed on every build, use your build pipeline’s image step. Graviton suits one-off batches, audits of existing assets and files you don’t want to upload anywhere.
What happens to transparent PNGs?
WebP, AVIF and PNG keep transparency, including semi-transparent edges. JPG has no transparency, so transparent areas become white.
How many images can I process?
Up to 250 per batch, and compressing is unlimited. A free account includes 3 downloads a day, reset at midnight UTC; Pro has no daily limit. Both plans have every format and setting.
Keep reading
Related guides
Optimize your site’s images
WebP at 1920 px is already set up. Your files stay on your device.
Open the website preset