Resource types are totalled separately; current values are compared with budgets, total variance and percentage share are calculated, and the largest controllable reduction opportunities are prioritised.
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Calculation tools
Web Performance Budget Planner
Collects resource budgets and current transfer sizes by type, calculating total variance, largest share, required reduction, and safety margin. It does not measure laboratory or real-user LCP, INP, or CLS.
✓ Free✓ No account✓ In-browser
QUICK ANSWER
What does this tool do?
Compare HTML, CSS, JS, image, and font kilobytes with a mobile transfer budget and produce a prioritised reduction plan.
APPLICATION AND DECISION GUIDE
Web Performance Budget Planner: method and usage
Collects resource budgets and current transfer sizes by type, calculating total variance, largest share, required reduction, and safety margin. It does not measure laboratory or real-user LCP, INP, or CLS.
current transfer KB for HTML, CSS, JavaScript, images, and fonts, plus per-type budgets, total budget, and safety margin Confirm the shape first with a small example containing no personal data.
a per-type budget table, total pass or fail state, KB reduction required, and a measurement plan
Practical steps
- Load the example or fill the clearly labelled fields for your scenario.
- Run the check on-device and review metrics, warnings, and recommended corrections together.
- Validate the result in the real target environment and record its assumptions.
comparing compressed transfer, main-thread time, and real LCP, INP, and CLS on critical routes with a cold cache and low-end mobile device
A transfer budget alone does not prove runtime performance or Core Web Vitals success. Measure lab and field data, third-party cost, and the user task separately.
Suitable use cases
- PR size gates
- Mobile start-up budgets
- Third-party script review
Worked decision record
Practical scenario: PR size gates. Compare HTML, CSS, JS, image, and font kilobytes with a mobile transfer budget and produce a prioritised reduction plan.
Against a 900 KB mobile budget, enter HTML 42, CSS 68, JS 310, images 460, fonts 96, and other 35 KB; then reduce images by 300 KB and compare headroom.
Acceptance record: comparing compressed transfer, main-thread time, and real LCP, INP, and CLS on critical routes with a cold cache and low-end mobile device. Keep the result-card metrics and warnings together with the retained example.
Do not publish in this state: A transfer budget alone does not prove runtime performance or Core Web Vitals success. Measure lab and field data, third-party cost, and the user task separately.
LEARN THE WORKFLOW
Guides for this tool
Performance Decisions with Web Vitals, Percentiles, and Queue Capacity
Replace a single average with route-level evidence, p75/p95, burst load, and asset budgets in one release gate.
Read guide →Safe Release Operations: From Performance Budgets to Restore Evidence
Turn performance, dependencies, backups, and change information into one reversible release decision instead of isolated checks.
Read guide →ABOUT THIS TOOL
Frequently asked questions
What input does Web Performance Budget Planner accept?+
current transfer KB for HTML, CSS, JavaScript, images, and fonts, plus per-type budgets, total budget, and safety margin Against a 900 KB mobile budget, enter HTML 42, CSS 68, JS 310, images 460, fonts 96, and other 35 KB; then reduce images by 300 KB and compare headroom.
What does Web Performance Budget Planner return?+
a per-type budget table, total pass or fail state, KB reduction required, and a measurement plan Acceptance record: comparing compressed transfer, main-thread time, and real LCP, INP, and CLS on critical routes with a cold cache and low-end mobile device. Keep the result-card metrics and warnings together with the retained example.
How should I validate Web Performance Budget Planner output?+
comparing compressed transfer, main-thread time, and real LCP, INP, and CLS on critical routes with a cold cache and low-end mobile device Do not publish in this state: A transfer budget alone does not prove runtime performance or Core Web Vitals success. Measure lab and field data, third-party cost, and the user task separately.
Does Web Performance Budget Planner send or store input on a server?+
Tool input is processed in the active tab. Saving to the Workstation or transferring to another tool is a separate choice. Consider browser extensions and shared devices separately; the privacy page explains advertising and network connections.