Resize Image Online Free — Change Dimensions Without Uploading
Change the dimensions of any JPG, PNG, or WebP image instantly in your browser — no upload, no account, completely free. Set an exact target size in pixels or scale proportionally by percentage. Lock the aspect ratio to prevent distortion, choose your output format, and download the result in seconds. A before-and-after preview shows both the original and resized image side by side.
Resize Result
How to Resize an Image Online
Alfreto's image resizer uses the browser's built-in HTML5 Canvas API to redraw your image at a new size using high-quality bicubic interpolation — entirely on your device. No file is ever uploaded to any server. The tool supports two modes: exact pixel dimensions for precise control, and percentage scaling for proportional resizing.
Step 1 — Upload Your Image
Click Choose Image or drag and drop a JPG, PNG, or WebP file into the upload area. Once loaded, the original image dimensions (width × height in pixels) are displayed automatically, and a preview of the original appears in the right panel.
Step 2 — Choose a Resize Mode
Select one of two modes from the tabs:
- 📐 Pixels mode — Enter an exact target width and/or height in pixels. Use this when you need a specific output size, such as 1280×720 for HD video thumbnails, 800×600 for email attachments, or 2480×3508 for A4 print at 300 DPI. The width and height inputs are pre-filled with the original dimensions as a starting point.
- 📏 Percentage mode — Use the slider to scale the image proportionally relative to its original size. 50% halves both width and height, 100% keeps the original dimensions, and 200% doubles the image. The resulting pixel dimensions are displayed live as you drag. This mode always preserves the aspect ratio automatically.
Step 3 — Set Aspect Ratio Lock (Pixels Mode)
In Pixels mode, the Lock aspect ratio toggle is on by default. When locked, changing the width automatically recalculates the height to maintain the original proportions — preventing stretching or distortion. Turn it off if you want to set a custom width and height independently (for example, to crop to a specific ratio). When unlocked, both inputs are editable independently.
Step 4 — Choose an Output Format
Select the file format for the resized output — independently of the input format:
- JPEG — Smallest file size, best for photographs. Uses lossy compression. No transparency support. The best choice when sharing online or by email where file size matters.
- PNG — Lossless quality, supports transparent backgrounds. Larger files than JPEG. Best for graphics, logos, screenshots, and images that must preserve exact pixel colors.
- WebP — A modern Google format that offers 25–35% smaller files than JPEG at equivalent quality. Supported by all modern browsers. The best choice for web use when file size and quality both matter.
Step 5 — Resize and Download
Click Resize. The Canvas API draws the image at the new dimensions using high-quality image smoothing. The result appears in the right panel alongside the original for comparison. Three stat cards show the original dimensions, new dimensions, and output file size. Click Download to save the resized image to your device.
Common Resize Use Cases
- Social media images — Instagram posts: 1080×1080 px. Twitter/X header: 1500×500 px. Facebook cover: 851×315 px. LinkedIn banner: 1584×396 px.
- Email attachments — Reduce a large photo to 800×600 or 1024×768 to keep under typical 10 MB attachment limits.
- Website images — Resize photos to the exact pixel width of the content column to avoid browsers scaling them and wasting bandwidth.
- Print preparation — At 300 DPI: A4 paper = 2480×3508 px. 4×6 inch photo = 1200×1800 px. 5×7 inch = 1500×2100 px.
- Thumbnails and avatars — Profile photos: 400×400 px square. Thumbnails: 150×150 or 300×300 px.
- Reducing file size — Scaling a 4000×3000 photo to 50% (2000×1500) reduces file size by approximately 75% without any quality compression.
Frequently Asked Questions
Is my image uploaded to a server?
No — your image never leaves your device. The tool uses the browser's built-in HTML5 Canvas API to load, redraw, and encode the image entirely within your browser tab. No data is transmitted over the internet at any point. This makes it safe for private, personal, or sensitive images.
What does "Lock aspect ratio" mean?
The aspect ratio is the proportional relationship between an image's width and height. When the lock is enabled, changing the width automatically recalculates the height to maintain the original proportions — preventing the image from appearing stretched or squashed. For example, a 1200×800 image with the lock on will automatically set the height to 533 if you change the width to 800. Disable the lock to set width and height independently for a custom crop ratio.
What is the difference between Pixels and Percentage mode?
Pixels mode lets you specify an exact output size — for example, exactly 1920 wide or exactly 1080 tall. Use this when you need to meet a specific dimension requirement (social media templates, print sizes, video thumbnails). Percentage mode scales the image proportionally — 50% makes it half as large in both dimensions, 200% doubles it. Use this when you want to reduce or enlarge without caring about the exact pixel count.
Will resizing reduce image quality?
Scaling down (making smaller) generally produces sharp results using high-quality bicubic interpolation. Scaling up (enlarging) will make the image appear softer or blurry, since pixel data is being stretched — no new detail can be added that was not in the original. For professional upscaling with AI-generated detail enhancement, dedicated AI upscaler tools are recommended. For everyday use — making an image slightly larger for a specific dimension requirement — the results are acceptable.
Can I resize a PNG and save it as JPEG, or vice versa?
Yes. The output format is completely independent of the input format. You can upload a PNG and save it as JPEG to reduce file size, upload a JPEG and save it as PNG for lossless quality, or convert any format to WebP for modern web optimization. The resize and format conversion happen in the same step.
Is there a maximum image size?
There is no server-imposed limit. The practical limit depends on your device's available memory. Very large images — over 20 megapixels or source files larger than 20 MB — may be slow to process or hit browser memory limits on lower-end devices. Output dimensions are capped at 16,000 × 16,000 pixels. For typical photos from smartphones and cameras (8–20 MP), processing is near-instant on any modern device.
Why is my resized file sometimes larger than the original?
This happens when you choose PNG output for a photo that was originally JPEG. PNG uses lossless compression, which is less efficient for photographic content — so a PNG of the same image is often significantly larger than a JPEG. It can also happen when you upscale (enlarge) an image and save it as a high-quality format. To get a smaller file, use JPEG or WebP output, or scale the image down rather than up.
Which browsers are supported?
The tool works in all modern browsers: Google Chrome, Microsoft Edge, Mozilla Firefox, and Safari. The Canvas API and WebP encoding are supported across all these browsers. For the best performance with large images, Chrome or Edge on a desktop computer is recommended.
Why Use Alfreto to Resize Images?
Most online image resizers require uploading your photo to a remote server — introducing privacy risks, upload wait times, and file size restrictions. Alfreto resizes images locally using your own browser, meaning your photo never leaves your device and resizing is instant regardless of your internet speed.