Why raster a vector into WebP at all
An SVG is already the ideal format for flat artwork on the web: small, sharp at any size, editable. The reason to convert one into WebP is almost always a platform that will not take SVG. Open Graph and Twitter card images must be raster. Most social networks, marketplaces, newsletter builders and app store listings reject SVG for security reasons, since an SVG can contain scripts. Many CMS media libraries strip or block the format for the same reason. WebP is the best general-purpose raster answer to that problem: it keeps transparency like PNG and produces files far smaller than PNG for the same image.
What happens between the vector and the pixels
The SVG is loaded into an image element in your browser and drawn onto a canvas at its intrinsic size, which comes from the width and height attributes on the root element. If those are missing the browser may use the viewBox, and failing that the tool defaults to 512x512. There is no scale option on this page, so set the attributes in a text editor before converting if you need a particular pixel size. The image context does not execute scripts or fetch external fonts, images or stylesheets, so text renders with whatever fonts your device has; convert text to outlines in the design tool to avoid surprises.
The canvas pixels are then handed to a Web Worker, where the libwebp encoder compiled to WebAssembly writes the final file. The alpha channel survives this step. Anti-aliased edges, drop shadows and semi-transparent fills all come through as 8-bit alpha in the WebP.
Lossy WebP on flat artwork
This page produces lossy WebP only. That sounds like the wrong choice for crisp vector graphics, but in practice flat colour areas cost almost nothing in WebP, and at high quality settings the encoder keeps edges clean. The slider runs from 20 to 95. For logos, icons and line art, use 85 to 95: the difference from a lossless PNG is not visible at normal zoom and the file is several times smaller. For illustrations with gradients and soft shading, 75 to 85 is enough. Below 60, thin outlines start to blur and faint halos appear around high-contrast edges. If you need exact pixels, SVG to PNG is the lossless option.
One subtlety: lossy WebP stores colour at reduced resolution (4:2:0 subsampling), so very thin coloured lines on a contrasting background, such as a one-pixel red rule on white, can look slightly soft. Brightness detail is kept at full resolution, so black text on white is unaffected.
A worked example with typical sizes
A 1600x900 flat illustration with a transparent background, 40 KB as SVG, typically becomes a WebP of 40 to 80 KB at quality 85, compared with 300 to 600 KB as PNG. A 1200x630 social preview card with a gradient usually lands around 50 to 90 KB. A 512x512 icon comes out at 8 to 20 KB. These are typical results for that kind of content, not guarantees, and complex artwork with fine texture will be larger.
Where the raster loses to the vector
Once rasterised, the image no longer scales cleanly, so keep the SVG as the master and generate WebP only for the specific size a platform needs. Older desktop software and a few email clients still cannot open WebP; if the destination is one of those, SVG to JPG is the compatible fallback, at the cost of transparency. For the smallest possible file on a modern site, SVG to AVIF goes further still. Nothing on this page leaves your device, and multiple SVGs can be converted in one batch, each downloading separately.