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Performance Budget Calculator

Calculate performance budgets for web assets.

ms

Largest Contentful Paint target

B

JavaScript bytes

B
B
B
Output will appear here…

How to Use This Tool

  1. Fill in Target LCP, JS Budget, CSS Budget, Image Budget, and Font Budget. Each control is labeled; you do not need to paste a JSON blob.
  2. Click "Calculate" to run the tool in your browser.
  3. Read the result below the form and copy it if you need it in another app.

Learn More About Performance Budget Calculator

About Performance Budget Calculator

Calculate performance budgets for web assets. Set byte limits to meet Core Web Vitals targets.

About

Calculate performance budgets for web assets. Set byte limits to meet Core Web Vitals targets.
Calculate performance budgets for web assets. Set byte limits to meet Core Web Vitals targets.
Runs in browser
Yes
No signup required
Yes

Examples

Typical 2.5s LCP budget (150KB JS).

Typical 2.5s LCP budget (150KB JS).
Input
2500, 150000, 50000, 200000, 80000
Output
Target LCP: 2500ms

── Budget breakdown ──
JavaScript: 146 KB
CSS: 49 KB
Images: 195 KB
Fonts: 78 KB
Total: 469 KB

── Time estimates (4G) ──
Download time: ~375ms
JS parse/compile: ~220ms
Estimated total: ~595ms

✓ Within 2500ms budget

Aggressive 1.8s LCP budget.

Aggressive 1.8s LCP budget.
Input
1800, 80000, 30000, 100000, 40000
Output
Target LCP: 1800ms

── Budget breakdown ──
JavaScript: 78 KB
CSS: 29 KB
Images: 98 KB
Fonts: 39 KB
Total: 244 KB

── Time estimates (4G) ──
Download time: ~195ms
JS parse/compile: ~117ms
Estimated total: ~312ms

✓ Within 1800ms budget

Relaxed 3s LCP budget.

Relaxed 3s LCP budget.
Input
3000, 200000, 60000, 300000, 100000
Output
Target LCP: 3000ms

── Budget breakdown ──
JavaScript: 195 KB
CSS: 59 KB
Images: 293 KB
Fonts: 98 KB
Total: 645 KB

── Time estimates (4G) ──
Download time: ~516ms
JS parse/compile: ~293ms
Estimated total: ~809ms

✓ Within 3000ms budget

Use Cases

  • Check performance budget calculator values while you draft a page, spreadsheet, or config.
  • Fill Target LCP, JS Budget, CSS Budget and compare the result to a second source.
  • Keep sensitive inputs on-device — this page runs the calculation in the browser.

Frequently Asked Questions

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