Bundle Size Impact Calculator

Gzip size is what actually gets transferred over the network. Minified size is what runs in the browser after decompression. Always measure gzip size when estimating download times — it's typically 60-80% smaller than the minified size. Tools like Bundlephobia report both values.

The standard lodash package bundles all 300+ utility functions. If you only use a few functions, you can use lodash-es (ES module version) with a tree-shaking bundler like webpack or Rollup, or import individual functions like `import debounce from 'lodash/debounce'`. This can reduce the impact from 26KB gzip to just 1-2KB.

Use Bundlephobia (bundlephobia.com) to get accurate sizes for any npm package. It reports minified, gzip, and download time estimates. For packages in your project, run `npx bundlesize` or use webpack-bundle-analyzer to see exact sizes after tree-shaking.

Google's Performance Budget guidelines suggest keeping the total JavaScript below 150-200KB (gzip) for fast load times on mobile 3G. For critical path JavaScript (what's needed to render the first screen), aim for under 50KB gzip. Large bundles cause poor Core Web Vitals scores.

Load time estimates assume 100% of the package is downloaded (no caching). Real-world performance depends on HTTP/2 multiplexing, CDN edge caching, browser caching on repeat visits, and device processing speed. A 40KB gzip download on 4G takes ~16ms transfer but parsing/execution may add 50-200ms on slower devices.