How to Measure SVG Optimization Properly: Raw Bytes, Gzip/Brotli, DOM Nodes, and Visual Diffs

The Four Numbers Worth Recording Before and After Optimization

1. Raw UTF-8 byte length: Reported live inside the SVG Nexus SVG Optimizer (which displays actual byte delta per file rather than generic estimates). Raw size matters for JS/HTML parse buffers and CSS Data URI length.
2. Compressed wire bytes (Brotli / Gzip): Removing 400 bytes of indented spaces may save only ~30 bytes after Brotli, whereas stripping unique 6-decimal path digits or embedded editor metadata saves real wire bytes because random decimals don't compress well!
3. Parsed DOM element count: Collapsing five nested <g> wrappers and unused <clipPath> nodes directly lowers browser memory and style-recalc work.
4. Visual fidelity at both 16px and 256px: A tiny byte count means nothing if rounding coordinates to 2 decimals warped a brand curve or stripped fill-rule="evenodd".

Reproducible Local Node.js Snippet to Measure Any SVG Folder

import fs from "node:fs";
import zlib from "node:zlib";

function inspectSvgPayload(filePath) {
  const buf = fs.readFileSync(filePath);
  const xml = buf.toString("utf8");
  const gzipBytes = zlib.gzipSync(buf, { level: 9 }).byteLength;
  const brotliBytes = zlib.brotliCompressSync(buf).byteLength;
  const tagCount = (xml.match(/<[a-zA-Z][^>]*>/g) || []).length;

  return {
    file: filePath,
    rawBytes: buf.byteLength,
    gzipBytes,
    brotliBytes,
    elementTags: tagCount,
  };
}

console.table([
  inspectSvgPayload("./before-export.svg"),
  inspectSvgPayload("./after-optimized.svg"),
]);

Always pair byte measurements with a side-by-side XML inspection in our Diff & Patch Studio so you know exactly which attributes or <defs> nodes were removed.