Images are usually the heaviest assets on a web page, and PNG - despite being lossless and widely supported - is rarely the most efficient way to ship them. WebP, developed by Google specifically to replace PNG and JPEG on the web, routinely cuts image weight by a quarter to a third with no visible quality loss. If your Largest Contentful Paint (LCP) score is being dragged down by images, this is usually the first place to look.
Why image format matters for Core Web Vitals
Google's Core Web Vitals measure real-world loading experience, and Largest Contentful Paint - the time it takes for the biggest visible element to render - is very often an image. A hero image or product photo saved as an uncompressed or lightly-compressed PNG can be several times larger than it needs to be, directly delaying LCP and hurting both user experience and search ranking signals.
Because image weight is one of the few performance levers a non-developer can pull directly (no code changes, no server work), converting existing PNG assets to a more efficient format is often the highest-leverage, lowest-effort performance fix available.
PNG vs WebP: technical differences
PNG uses lossless DEFLATE compression - it preserves every pixel exactly, which is ideal for graphics with sharp edges, transparency, or text, but produces larger files for photographic content. WebP supports both lossless and lossy compression modes, uses more modern prediction and entropy-coding techniques than PNG, and supports alpha transparency in both modes - meaning it can usually replace PNG without giving up transparency support.
In lossy mode (the default for most converters, including our PNG to WebP converter), WebP intelligently discards visual information humans are unlikely to notice, similar to JPEG but with a more efficient algorithm - which is why it consistently produces smaller files at comparable visual quality.
How much smaller is WebP really
Independent benchmarks and Google's own testing consistently show WebP producing files 25–35% smaller than equivalent-quality PNGs, and around 25–30% smaller than JPEGs at the same visual quality. The exact number depends heavily on image content: photographs with lots of gradients and detail compress more dramatically than flat-color graphics or line art, where PNG's lossless approach is already fairly efficient.
For a page with several large images, this routinely translates to hundreds of kilobytes of savings - often enough to move an LCP score from "needs improvement" to "good" without touching any code.
Converting PNG to WebP in your browser
Conversion doesn't require design software. A browser-based converter reads the PNG's decoded pixel data using the Canvas API, then re-encodes it as WebP using canvas.toBlob() with the WebP MIME type - the same underlying mechanism your browser already uses to display images, just run in reverse to produce a new file. Drop your PNG into the converter, and the WebP download is typically ready in under a second, with no upload and no quality settings to fumble.
The same approach works for JPG to WebP conversions, useful for photo-heavy pages where images were originally saved as JPEG.
Browser support and fallbacks
WebP is supported by every major browser released in the last several years - Chrome, Firefox, Safari, and Edge all support it natively, covering well over 95% of global traffic. For the rare older browser that doesn't, the standard approach is a <picture> element with a WebP <source> and a PNG or JPG fallback <img>, letting the browser pick whichever it supports. In most modern projects, a plain WebP <img> tag is now perfectly safe on its own.