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.
Calculations run locally in your browserTool
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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