Frontend Engineering Tools
JavaScript Bundle Size Calculator
Enter total JS and CSS bundle sizes to assess against 3G performance budget targets with parse time estimates.
No data is transmitted — everything runs locallyTool
Example — Representative default scenario — total js KB 320 · total css KB 45 · connection 3G.
Total bundle
365 KB
JS: 320KB + CSS: 45KB
JS vs budget
+150 KB
Google budget: 170KB (gzip)
Parse+load on 3G
1.90s
at 1.5Mbps
Status
⚠ Over budget
About this tool
JavaScript Bundle Size Calculator
The JavaScript Bundle Size Calculator assesses gzipped bundle size against connection-based budgets and estimates parse time on mid-tier mobile devices.
• Check if current bundle size exceeds Google's 170KB JS recommendation
• Estimate JS parse time on mid-tier mobile before a performance review
• Calculate bundle budget headroom before adding a new dependency
• Identify whether JS or images are the bigger performance bottleneck
Affiliate disclosure
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FAQ
What does this tool tell you?
The JavaScript Bundle Size Calculator assesses gzipped bundle size against connection-based budgets and estimates parse time on mid-tier mobile devices.
What affects the result most?
JavaScript budget: <170KB (gzip) for total JS on 3G — Google recommendation. Parse time: 1MB JS takes ~3.5s to parse on mid-tier mobile — parsing is CPU-bound. Code splitting: route-based splitting — load only JS needed for current page.
How should I use the result?
The calculation is deterministic — the same inputs always produce the same output — so the most useful workflow is to vary one input at a time and see which factor moves the result most. That tells you where to focus your attention before committing to a decision.
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