Free tool · JPG · Runs in your browser
Convert an image to 21:9
Short answer
Choose one or more images and the tool scales each one until it fills 2560 × 1080, cuts the excess from the center and saves a JPG at quality 0.92, with a white background under any transparency. Nothing is stretched. On our six test pictures the results were 312 KB to 739 KB and each took 31 to 38 ms. Nothing is uploaded, and several files come as one ZIP.
Batch is unlimited and free - every image is processed on your device, so there is no queue and no daily cap.
Key takeaways
- The crop keeps the middle: a 3840 × 3877 photograph keeps 42% of its area in 21:9, a wide 3827 × 1588 scan keeps 98%.
- 3 pictures are smaller than the frame and are enlarged (2122 × 2644 by 1.21×, 1060 × 1320 by 2.42×, 640 × 480 by 4.00×); enlarging adds no detail, so start from the largest file you have.
- The output is always a JPG at quality 0.92: 312 KB to 739 KB here. A PNG with transparency gets a white background.
- Fidelity: the results scored SSIM 0.91 to 0.98 against a Lanczos crop of the same picture, which is the combined effect of the browser's resampling and the JPG.
- No platform in our registry lists 21:9 as its preferred shape, but it is a common editing shape.
Measured: six pictures to 21:9
Measured in headless Chromium with the tool's own steps: a white background, a cover crop with drawImage, and toBlob at quality 0.92. Test pictures are public domain NASA scans and a PNG graphic, plus a small picture made from one of them. SSIM compares each result with a Lanczos crop of the same picture made by ffmpeg (1.0 would be identical). Other browsers use their own encoders, so sizes can differ.
| Picture | Pixels | Scale before the crop | Picture kept | Result size | Time | SSIM |
|---|---|---|---|---|---|---|
| Photo, nearly square | 3840 × 3877 | 0.67× | 42% | 739 KB | 38 ms | 0.91 |
| Portrait, 4:5-like | 2122 × 2644 | 1.21× | 34% | 432 KB | 34 ms | 0.94 |
| Wide document scan | 3827 × 1588 | 0.68× | 98% | 637 KB | 38 ms | 0.92 |
| Square PNG graphic | 5380 × 5432 | 0.48× | 42% | 482 KB | 37 ms | 0.91 |
| Small portrait (1060 px) | 1060 × 1320 | 2.42× | 34% | 312 KB | 34 ms | 0.98 |
| Small landscape (640 px) | 640 × 480 | 4.00× | 56% | 348 KB | 31 ms | 0.97 |
2560 × 1080.
The size follows the amount of detail and the frame: 2560 × 1080 holds 2.76 megapixels, so the same picture gives a different file for each ratio.
The same pictures in every ratio
For comparison, the result size of each test picture in all six shapes. The frame sizes are the ones the pages use.
| Picture | 9:16 (1080 × 1920) | 16:9 (1920 × 1080) | 1:1 (1080 × 1080) | 4:5 (1080 × 1350) | 4:3 (1440 × 1080) | 21:9 (2560 × 1080) |
|---|---|---|---|---|---|---|
| Photo, nearly square | 556 KB | 567 KB | 383 KB | 444 KB | 462 KB | 739 KB |
| Portrait, 4:5-like | 401 KB | 371 KB | 252 KB | 306 KB | 309 KB | 432 KB |
| Wide document scan | 494 KB | 497 KB | 304 KB | 379 KB | 387 KB | 637 KB |
| Square PNG graphic | 536 KB | 444 KB | 274 KB | 326 KB | 376 KB | 482 KB |
| Small portrait (1060 px) | 307 KB | 274 KB | 210 KB | 252 KB | 242 KB | 312 KB |
| Small landscape (640 px) | 273 KB | 318 KB | 204 KB | 229 KB | 261 KB | 348 KB |
21:9 is a larger frame than the others here (2.76 megapixels), which shows in the size column.
What the tool does to the picture
For each file the tool computes one scale: the larger of the frame width over the picture width and the frame height over the picture height. It fills the frame with white, draws the picture at that scale, centered, so the excess falls outside the frame, and saves the canvas as a JPG at quality 0.92. MDN describes drawImage with a destination size as scaling the source to fit it, and toBlob quality as a number between 0 and 1 for lossy formats.
Crop or add bars?
Cropping fills the frame; for a picture of a different shape some of it is lost. A square photograph keeps 42% of its area in 21:9. If the whole picture must stay visible, resize it to fit inside the frame and add a background instead of cropping.
Free tools:Compress an imageCompress an image to a target sizeRemove the background from an imageConvert a video to 21:9Convert an image to 9:16Convert an image to 16:9Convert an image to 1:1
Where 21:9 is used
Ultrawide cinematic - used for trailers and letterboxed film looks.
None of the platforms in the registry names 21:9 as its preferred shape; check the destination's own spec.
Questions people ask
How do I resize an image to 21:9?
Choose the picture above. The tool scales it to cover 2560 × 1080, crops the center and gives you a JPG.
Will the picture be stretched?
No. It is scaled in proportion and the excess is cut from the center.
Can I convert several images at once?
Yes. Several files are converted one after another and offered as one ZIP.
What happens to transparency?
The result is a JPG, so transparent areas are filled with white.
What quality does it save at?
JPG at quality 0.92. To reach a file size limit, use the target size tool afterwards.
Is my image uploaded?
No. It is processed in your browser.
Why does a small picture look soft?
A picture smaller than 2560 × 1080 is enlarged to fill the frame, which adds no detail. Start from a larger file.
Can I choose which part is kept?
No, the center is kept. Crop the picture first if the subject is off center.
Related
Sources and how we checked
- MDN: CanvasRenderingContext2D.drawImage() (read 2026-10-09)
- MDN: HTMLCanvasElement.toBlob() (read 2026-10-09)
- Wikimedia Commons: Buzz salutes the U.S. Flag (NASA, public domain), one of the photographs used (read 2026-10-09)
Reviewed October 9, 2026. The measurements ran the tool's own canvas steps in headless Chromium. The script and the results are in data/seo/hub/evidence/2026-10-09/aspect.