Complete Guide to Using the Image Resizer Online

One Resizer helps you resize photos, signatures and other images in your browser. Set dimensions in pixels, centimetres, millimetres or inches, choose a supported output format, and optionally try to meet a target file size. Always follow the dimensions and file-size limits stated by the institution or website receiving your image.

What is an online image resizer?

Image resizing changes an image's pixel width and height. Pixel dimensions describe the number of pixels in the image, while centimetres, millimetres and inches describe a physical size calculated using the selected DPI. Resizing does not automatically remove a background or change the subject's appearance beyond scaling and encoding.

How to resize an image online

1. Choose an image or drag it into the upload area.
2. Review the original dimensions, file size, format and aspect ratio.
3. Select PX, CM, MM or IN as the dimension unit.
4. Set the DPI value when using physical units.
5. Enter the desired width and height.
6. Keep the aspect-ratio option enabled to preserve proportions, or disable it only when stretching is acceptable.
7. Optionally enter a target file size such as 20 KB, 25 KB, 40 KB or 100 KB.
8. Select Keep Original Format, JPEG, PNG or WebP.
9. Adjust quality for JPEG or WebP output if needed.
10. Press Resize Image, then verify the displayed output dimensions, actual size and target status.
11. Preview and download the result.

Understanding the three panels

Original Image: shows the source preview, pixel dimensions, file size, format and aspect ratio. Use Choose Different Image to start with another file.

Resize Controls: includes dimension unit, DPI, width, height, aspect-ratio lock, optional target size, KB/MB selector, quick presets, image quality and output format. The presets fill the target-size field; processing is not complete until you press Resize Image.

Live Result: shows the output preview and reports output dimensions, actual file size, format and whether the target was reached. Reset Settings clears the current output and returns the controls to the source image dimensions.

Resizing an image to a specific KB size

Enter a number such as 20, 25, 40 or 50 and choose KB, or select a preset. The final file size depends on the image dimensions, image detail, format and quality. JPEG mode attempts to encode the image below the requested target and may add trailing bytes when the encoded image is smaller, allowing the downloaded file to reach the requested byte count without changing decoded pixels. This technique is format-specific; PNG and other formats do not receive the same exact-size treatment. If the image cannot be encoded below the target, the tool reports that the target was not reached.

Passport photo and signature resizing

Check the application instructions before resizing a passport photo or signature. Different exams, institutions and government forms can require different dimensions, DPI, formats and maximum file sizes. Enter the required values exactly. A correct size alone does not guarantee acceptance, and resizing does not remove a photo background.

Image formats and quality

• JPEG/JPG: suitable for many photographs; it does not preserve transparency. Transparent areas are filled with white when this tool creates JPEG output.
• PNG: lossless and supports transparency. The quality slider may not change PNG output size.
• WebP: a modern format that can provide compact files; compatibility depends on the destination website or form.
• Keep Original Format: uses the original JPEG, PNG or WebP format when supported.

Privacy and browser-based processing

Your selected image is processed in your browser by this tool and is not sent to One Resizer's image-processing server by the resizing workflow. Other website services, such as hosting, analytics or advertising, may operate separately according to their own settings and policies. Processing uses browser-side JavaScript and the Canvas API, so performance depends on your device, browser and image size.

Troubleshooting

• Image will not open: use a valid JPEG, PNG or WebP image and try another browser if needed.
• File is too large: this page accepts files up to 25 MB; choose a smaller file if it exceeds the limit.
• Output is too large: reduce dimensions, choose JPEG/WebP, or lower the quality setting.
• Target size was not reached: try smaller dimensions or a lower JPEG quality. Some targets are not feasible for every image.
• Dimensions change when units change: physical units are converted using the selected DPI; pixel values may be rounded.
• PNG size does not respond to quality: PNG is lossless and may ignore the quality control.
• Download does not start: resize first, then press Download; check whether your browser blocks downloads.
• Image looks stretched: enable Maintain Proportional Aspect Ratio and resize again.
• Mobile controls are cramped: use portrait orientation and scroll vertically; controls stack on narrow screens.