Convert PNG to WebP — alpha intact, files dramatically smaller

Why convert PNG to WebP?

PNG was designed for lossless compression with full alpha support, and it does that job well. The problem is byte count. A 1024x1024 transparent logo exported from Figma often lands at 250-300 KB even after running through an optimizer like pngquant. The same image as lossless WebP weighs around 200-215 KB — a 25% reduction with absolutely zero pixel change. Switch to lossy WebP at quality 90 and the file drops to roughly 75-80 KB, still transparent, still indistinguishable to the human eye in normal viewing conditions. For mobile-first web apps and Core Web Vitals budgets, that difference compounds fast across a sprite sheet or an icon library with dozens of assets.

What you lose and what you gain

WebP lossless mode is a strict upgrade over PNG: every pixel is preserved exactly, the alpha channel is intact, and the file is smaller. There is no quality trade-off at all — lossless is lossless. Lossy WebP-with-alpha is a different story. At quality 90 or above the differences are microscopic — a few tenths of a percent SSIM — but at the very edges of semi-transparent pixels, the encoder may introduce very faint fringing that a sharp-eyed designer will spot in a side-by-side at 400% zoom. At quality 75, that fringing becomes visible at normal zoom on hairline edges. The practical rule: use lossless if you are distributing design source assets or working in a pipeline where re-encoding will happen later. Use lossy (q90+) for final web delivery where you control the output. Both modes keep the alpha channel working in every modern browser.

How to convert PNG to WebP

The entire conversion runs locally in your browser. No file is ever uploaded to a server, and the tool works offline after the first visit. Here is the full process:

1. Click "Convert to WebP →" at the top of this page, or drag your PNG file onto the drop zone on the homepage. Multiple formats are accepted but PNG is decoded natively by the browser with no extra WASM needed.
2. ConvertMyPic uses the browser's built-in PNG decoder (the same path as an <img> tag) to load the image into a canvas, preserving the full RGBA pixel data including the alpha channel.
3. Google's libwebp, compiled to WebAssembly, encodes the canvas pixels to WebP. By default the tool uses lossy mode at quality 90, which gives the best size-to-fidelity ratio for most transparent assets. Toggle the lossless switch on the /convert page if you need bit-exact output.
4. Use the quality slider (1–100) to dial in the size/fidelity balance. Quality 90 is the recommended starting point for web-shipped assets. Quality 100 in lossy mode is near-lossless but not identical to the PNG lossless output; for true lossless, flip the dedicated toggle.
5. Click the download button. The WebP file saves to your Downloads folder with the extension swapped — logo.png becomes logo.webp. File name and directory structure are not changed. You can immediately drop it into your web project or CDN.

File size comparison: PNG vs WebP at different modes

Representative sizes for two common transparent-asset scenarios. Measured with libwebp 1.4 for the WebP outputs; PNG sizes are post-pngcrush.

When to convert, and when to stay on PNG

Stay on PNG when you are distributing design source files that other people will edit in Figma, Photoshop, or Affinity Designer — those tools round-trip PNG without loss, and WebP support in design tooling is still inconsistent as of 2026. Stay on PNG when your audience includes Internet Explorer users (IE never shipped WebP support) or old versions of Edge (pre-Chromium, which lost WebP in some rendering paths). Stay on PNG for any image that will be re-encoded again later; each lossy pass accumulates artifacts, and PNG stops that clock. Switch to WebP for anything you are deploying on the public web and do not expect to edit further. Logos, hero backgrounds with transparency, icon sprites, UI decoration, and marketing overlays are all ideal candidates. WebP is the right choice when you are targeting mobile-first or low-bandwidth users, when you are building a Progressive Web App and every kilobyte in the cache budget matters, or when Lighthouse / Core Web Vitals is flagging your PNG payloads. Browsers that receive WebP as part of an `<img srcset>` or via a `Content-Type: image/webp` response header handle it identically to PNG — no extra code required.

Under the hood: which codecs are used

PNG decoding is handled by the browser itself via a canvas element — this is the same high-performance native path used to render every PNG image on the web, so no additional WebAssembly is downloaded for the decode step. WebP encoding uses libwebp, the reference implementation maintained by Google at chromium.googlesource.com/webm/libwebp. ConvertMyPic ships a WebAssembly build of libwebp so the encoder runs at near-native speed inside a Web Worker, keeping the UI responsive during large encodes. Both lossless and lossy-with-alpha paths use the same libwebp binary — the mode is toggled via an encoder flag. The WASM module is cached by the service worker after the first page load, so subsequent conversions work entirely offline.