Image Resizer, Resize Photos Online
Resize images by width, height or percentage, lock the aspect ratio and pick a fit mode. 100% in your browser, no uploads.
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Frequently asked questions
Are my images uploaded to any server?
What is aspect ratio and why should I lock it?
What is the difference between Contain, Cover and Stretch fit modes?
Can I resize an image by percentage instead of fixed pixels?
What formats are supported as input and output?
Is there a maximum resolution or file size?
Why should I serve multiple image sizes on a website?
Does resizing affect image quality?
What does megapixel mean and why does it matter?
How does browser-side resizing compare to Photoshop or other desktop tools?
About Image Resizer, Resize Photos Online
Resizing an image means changing the number of pixels that make up its width and height, which in turn affects both the file size and how the image displays on screen. A digital image's resolution is measured in megapixels — a 4000 × 3000 image contains 12 million pixels. Halving both dimensions to 2000 × 1500 reduces the pixel count to 3 million, cutting the raw data by 75 %. Understanding the difference between an image's intrinsic pixel dimensions and the CSS size at which a browser renders it is essential for web performance: an image that is 4000 px wide but displayed in a 400 px container forces the browser to download ten times more data than necessary.
Web developers, graphic designers, social media managers, and bloggers all resize images daily. A responsive web design typically requires the same photograph at three or four different widths — a full-resolution original for large monitors, a medium variant for tablets, and a compact thumbnail for mobile — served via the HTML srcset attribute so browsers download only the size they need. E-commerce platforms need consistent thumbnail dimensions for product grids. Email marketers must keep images below strict size caps. Print workflows require specific DPI and millimetre targets. The single act of resizing to the right dimensions before upload can save gigabytes of storage and dramatically speed up page loads.
This tool performs every resize operation locally in your browser using the HTML Canvas API, so your images never leave your device. You can specify an exact target width, an exact height, or a percentage of the original dimensions. Enabling the aspect-ratio lock ensures the image is never stretched or squashed. Three fit modes give you fine-grained control: Contain scales the image to fit entirely inside the target box (the canvas is padded if necessary), Cover fills the box and crops the overflow from the edges, and Stretch forces the image into the exact dimensions regardless of proportion. The result is available as a PNG, JPEG, or WebP download at whatever quality you choose.
A few tips for best results: always lock the aspect ratio unless you specifically need a distorted output. When generating thumbnails for a website, aim for the exact display size rather than relying on CSS to scale down — serving correctly sized images is one of the quickest wins in a Lighthouse performance audit. If you need to produce multiple sizes of the same image, resize to the largest first, then resize that output down to the smaller sizes, as this preserves more detail than repeatedly downscaling from the original. For retina and high-DPI displays, produce images at 2× the CSS display size to ensure crisp rendering.
Pixels, Megapixels, and the Long Road to Responsive Images
The word "pixel" is a portmanteau of "picture element" and was coined in the late 1960s by engineers at NASA's Jet Propulsion Laboratory who needed a term to describe the individual cells of digitised images returned by space probes. The first consumer digital camera capable of capturing a full megapixel was the Kodak DCS 100, released in 1991 at a price of around $13,000 — it stored images on a separate hard-drive unit worn on a shoulder strap. By 2010, budget smartphones were shipping with 5-megapixel cameras, and by 2023, flagship phones routinely exceeded 200 megapixels, creating a paradox where the cameras in our pockets produce images far larger than any screen can display.
The concept of responsive images — serving different image sizes to different devices — predates the modern web by decades. Early television broadcast engineers faced an analogous problem when designing systems that had to work on screens ranging from tiny portable sets to large living-room consoles. On the web, the problem became acute around 2010 when Apple introduced the Retina display, which doubled the pixel density of the iPhone 4 screen. Developers suddenly had to serve images at twice the resolution for these devices or accept blurry photos, while not penalising regular-screen users with unnecessarily large downloads. This tension drove the creation of the HTML srcset attribute, standardised in 2014, and the picture element, both of which allow browsers to select the most appropriate image size automatically.
Before digital zoom existed, optical zoom in cameras was achieved by physically moving lens elements — the same principle that telescope makers had used since the 17th century. Digital resizing algorithms, by contrast, are a product of signal-processing mathematics developed in the 20th century. The bilinear interpolation method used by most browsers today was described in a 1975 paper, while bicubic interpolation — favoured by professional image editors — was introduced by Robert Keys in 1981. Modern AI-based upscaling tools use convolutional neural networks trained on millions of image pairs to "invent" plausible detail when enlarging images, producing results that older mathematical methods simply cannot match.