Image Resizer
Resize and convert images privately in your browser. Free. No signup required.
Resize your image
INSTANT · FREEChanging either dimension adjusts the other to preserve the original proportions. Your image stays on your device. Browser memory limits apply.
How to use this image resizer
Change an image’s pixel dimensions and choose a JPG, PNG or WebP output. Processing happens in your browser, so the selected image is not uploaded to Prontiko.
- Choose a JPG, PNG or WebP image from your device.
- Leave Keep original aspect ratio enabled to preserve the image’s proportions.
- Change the width or height in pixels. With the ratio enabled, the other dimension updates automatically.
- Choose an output format and download the resized image.
How the resize is calculated
- With the original ratio locked: new height = new width × original height ÷ original width
- Pixel dimensions are rounded to whole numbers
Resize a landscape photo without stretching it
Original: 2400 × 1600 px · New width: 1200 px · Keep original aspect ratio: enabled
- New dimensions
- 1200 × 800 px
- Original ratio
- 3:2
Halving the width also halves the height. The photo keeps the same proportions. Turning off the ratio lock lets you choose both dimensions independently, which can stretch the image.
Useful to know
Output is limited to 12,000 pixels per side and 40 million pixels in total. A device may run out of memory below those limits. Enlarging a small image adds pixels but cannot recover detail that was not in the original.
Frequently asked questions
Is my photo sent to a server?
No. The resizer uses your browser to read and process the selected file. The image is not uploaded to Prontiko, and the result downloads directly to your device.
Why does the height change when I edit the width?
Keep original aspect ratio is enabled. The height adjusts using the proportions of the original image, with rounding to a whole pixel. Turn the option off if you need to enter both dimensions independently.
Which output formats keep transparency?
PNG and WebP can preserve a transparent background. JPG does not support transparency, so transparent areas are filled with white when you choose JPG.
Can I crop the image or guarantee a smaller file size?
This tool resizes the entire image and does not crop it. A smaller pixel size often reduces file size, but the output format and image content also affect the result. It does not target a specific number of kilobytes.