How does the aspect ratio lock work?

When Lock Aspect Ratio is enabled, typing a new width calculates the proportional height using the original width-to-height ratio. Typing a new height recalculates width in the same way. This keeps objects and people from appearing distorted.

What happens if I enter dimensions larger than the original picture?

The canvas scales the image up to your chosen width and height using browser image smoothing. This enlarges existing pixels, but it cannot recreate fine optical detail that was not in the original photo.

What background color appears if I export a transparent image as JPEG?

In our browser test, exporting a transparent PNG as JPEG through this resizer produced a solid black (#000000) background because JPEG does not support transparency. Choose PNG or WebP if you want to keep transparency.

What image resolution limits apply in the browser canvas?

In our test on Chromium, the 2D canvas context supported dimensions up to 32768 pixels. We also tested resizing 6000x4000 and 8000x6000 JPEGs down to half size in browser memory without errors.

Are my images uploaded to a server?

No. The entire resizing process runs on your computer or mobile device inside your browser sandbox. Files are never uploaded over the network.

Free & Private Online Browser Utility

Resize Image

Resize JPEG, PNG, and WebP images in your browser without uploading files across the network. The tool uses standard HTML5 Canvas 2D methods to scale pixel dimensions up or down. Enter pixel values directly, toggle the aspect ratio lock, or select commonly used size presets for social platforms.

How to use

Step 1: Choose an image file

Drop an image into the upload zone or click to select a file from your device. The tool accepts JPEG, PNG, and WebP files.
Step 2: Set your target dimensions

Enter target pixel values in the width or height fields. Turn on the Lock Aspect Ratio switch to update both sides proportionally, or click a preset button.
Step 3: Select export format and quality

Pick your export format (Original, PNG, JPEG, or WebP). If selecting JPEG or WebP, adjust the quality slider between 10% and 100%.
Step 4: Download the resized image

Click Resize Image to draw and encode the image in browser memory. Click Download to save the file to your computer or phone.

Options explained

Lock Aspect Ratio Switch

Maintains the proportion between width and height. Entering a new width recalculates height automatically, and entering a new height recalculates width.

When to use: Keep active for photos and portraits to avoid stretching or distorting image subjects.

Percentage Scaling Buttons

Calculates proportional dimensions at 25%, 50%, 75%, 100%, 150%, or 200% of the loaded image's original pixel dimensions.

When to use: Use for quick reductions when preparing images for email attachments or messaging.

Social Media Dimension Presets

Supplies commonly used platform dimensions such as Instagram Square (1080x1080), Instagram Story (1080x1920), YouTube Thumbnail (1280x720), Twitter Header (1500x500), LinkedIn Banner (1584x396), Facebook Cover (820x312), Full HD 1080p (1920x1080), and 4K Ultra HD (3840x2160). Applying a preset disables the ratio lock so the image matches the target frame exactly.

When to use: These are commonly used sizes; check the platform for current requirements before final publishing.

Export Format Selector

Chooses the output image format: Original format, PNG, JPEG, or WebP.

When to use: Choose PNG if you need transparent backgrounds; choose JPEG or WebP for photos.

Quality Slider

Controls lossy quantization for JPEG and WebP between 10% and 100% (default 90%).

When to use: Lower the slider to reduce file byte size; raise it to preserve visual detail.

Worked example

Input: Repository sample photo (sample-photo.jpg at 1376x768 resolution, 450,169 bytes)

Output: Resized 1376x768 sample image (450,169 bytes) to 50% scale (688x384 pixels) at quality 0.9 producing 34,317 bytes (33.5 KB)

Example from repository test; results depend on your input file dimensions and chosen settings.

Tips & limits

Downscaling reduces file size because fewer pixels are stored in the output file.
Upscaling enlarges existing pixel data through canvas smoothing; it does not add new optical detail captured by a camera.
Turning off the aspect ratio lock allows custom width and height, but non-uniform scaling will stretch or compress objects in the picture.
If you export a transparent PNG as JPEG in this resizer, the browser encodes transparent areas over a solid black (#000000) background.
Tested with 12 MP (4032x3024) photos on our 6-core Intel desktop running Chromium: 5 photos took 1,375 ms, 10 took 1,292 ms, 25 took 2,921 ms, and 50 took 6,762 ms; throughput varies depending on your CPU, RAM, and image resolution.

Common problems

The resized picture looks stretched or squashed: Turn the Lock Aspect Ratio switch on before typing dimensions, or use the percentage buttons to scale width and height together.
Exporting a transparent image as JPEG produced a black background: JPEG does not support transparency. To preserve transparent areas, set the export format to PNG or WebP.
The output file is larger than the original file: If you convert a heavily compressed JPEG into a PNG or export at 100% quality, the new file can require more bytes. Lower the quality slider or choose JPEG output.
The browser tab feels slow when opening very large camera files: Large photos require uncompressed memory while open in the browser. Resize very large camera images one file at a time.

Frequently Asked Questions (FAQ)

How does the aspect ratio lock work?: When Lock Aspect Ratio is enabled, typing a new width calculates the proportional height using the original width-to-height ratio. Typing a new height recalculates width in the same way. This keeps objects and people from appearing distorted.
What happens if I enter dimensions larger than the original picture?: The canvas scales the image up to your chosen width and height using browser image smoothing. This enlarges existing pixels, but it cannot recreate fine optical detail that was not in the original photo.
What background color appears if I export a transparent image as JPEG?: In our browser test, exporting a transparent PNG as JPEG through this resizer produced a solid black (#000000) background because JPEG does not support transparency. Choose PNG or WebP if you want to keep transparency.
What image resolution limits apply in the browser canvas?: In our test on Chromium, the 2D canvas context supported dimensions up to 32768 pixels. We also tested resizing 6000x4000 and 8000x6000 JPEGs down to half size in browser memory without errors.
Are social media dimensions up to date?: The preset buttons use commonly used sizes; check the platform for current requirements before uploading.
Are my images uploaded to a server?: No. The entire resizing process runs on your computer or mobile device inside your browser sandbox. Files are never uploaded over the network.

How to use

Step 1: Choose an image file

Step 2: Set your target dimensions

Step 3: Select export format and quality

Step 4: Download the resized image