Image Size Converter — Resize JPG, PNG, WebP in Your Brow...

How to use the image size converter

Drop files into the zone. JPG, PNG, and WebP are accepted; other types show an error on that row but do not stop the batch.
Pick target dimensions. Type a width and height. Toggle the padlock to keep the W:H ratio when you change one of them.
Quality + format. The Quality slider applies to JPG and WebP output. PNG output is always re-encoded losslessly. Pick Keep original to stay in the source format, or All to WebP to convert everything.
Resize all. Each image is fit inside the target box. Mixed-aspect batches work fine — each image keeps its own aspect ratio.
Download. Save individual files or grab a ZIP of everything.

How “fit inside” works

The tool uses what designers call contain fit. Imagine the target dimensions as a bounding box. Each image is scaled to fit fully inside that box. If your image is wider than the target, it scales down until its width matches; if taller, it scales down until its height matches. No cropping, no stretching, no padding — just a smaller copy of your image, no larger than your target on either axis.

Example: target 1280×720, source 4000×3000 (4:3 photo). The output is 960×720 — the height fills the box, the width is whatever the 4:3 aspect demands.

If you need exact target dimensions with cropping, this tool does not do that. Use a dedicated cropper or an image editor.

Common target sizes

Web hero: 1920×1080 or 1600×900.
Social card (Twitter/Facebook/LinkedIn share): 1200×630.
YouTube thumbnail: 1280×720.
Instagram square: 1080×1080.
Email-friendly attachment: 1024 on the longest side.
Avatar/profile: 512×512 or 256×256.

Type any of these into the dimension boxes; the tool handles the rest.

Why Lanczos-3 matters

The browser’s built-in canvas drawImage uses fast but coarse resampling (typically bilinear). It is fine for thumbnails on the page, but the output looks softer than the source. Lanczos-3 is a higher-order kernel that preserves sharp edges and fine detail at the cost of more CPU. The tool runs it in WebAssembly — the difference is invisible on small images and very visible on large ones with fine text or detail.

Quality vs file size

For JPG and WebP outputs, the Quality slider trades visual quality for byte size:

95–100: visually indistinguishable from the source, but barely smaller than the original.
85–90: visually lossless to the human eye in almost all cases. Default value of 85 is a good baseline.
70–85: noticeable compression artifacts only on close inspection. Best for web bandwidth.
Below 70: visible artifacts.

PNG output ignores the slider — PNG is always re-encoded losslessly.

Privacy

Same posture as the other tools: a static HTML page that loads its JavaScript and WebAssembly from this domain, and runs everything in your browser tab. The Network tab in DevTools confirms it — once the codecs load, no further requests fire. There is no upload, no temporary cloud storage, no analytics on file content.

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Frequently asked questions

How does aspect-ratio lock work?

When the padlock is closed, changing either the width or the height updates the other to keep the W:H ratio you set when you toggled the lock. With multiple files of different aspect ratios, the tool uses each image's own aspect to fit inside your target box — so no image is stretched or cropped.

What does "fit inside" mean?

Each image is scaled to fit fully inside the width × height box you set, preserving its own aspect ratio. The output may be smaller than the target on one axis if the source aspect differs. No pixels are cropped, no pixels are added.

Does my image leave my browser?

No. Decode, resize, and re-encode all happen client-side using WebAssembly codecs. Open DevTools → Network — after the codecs download (once), no further requests fire. Your images stay on your device.

Which resampling algorithm does it use?

Lanczos-3, via the jsquash WASM port. It is the same algorithm used by professional image tools and gives sharp downscales without the blurry look you get from default browser resampling.

Can I upscale images?

Yes — set a target larger than the source. Quality will degrade because no new detail is invented; Lanczos-3 just interpolates smoothly. For best results, never upscale by more than 2× and avoid upscaling JPGs that are already compressed.

Will the output be smaller in bytes?

Usually yes, because the resized image has fewer pixels. The Quality slider controls JPG/WebP byte size on top of that. PNG keep mode is lossless re-encoding, so very simple images may stay the same size.

What happens to image metadata (EXIF, ICC profile)?

Stripped. The decode-then-re-encode pipeline does not preserve EXIF, GPS, or ICC color profiles. If you need those, do not resize with this tool — they will be lost.

How big can the batch be?

Limited by browser memory. A dozen 10-megapixel photos resize cleanly on a typical laptop. Hundreds of files in one batch may slow the page; split them in that case.

Why does the first resize feel slow?

The resize codec and each format codec (JPEG, PNG, WebP) are WebAssembly modules that download and initialize on first use. After the first file of each format, every subsequent resize is fast.