Performance Budget Calculator | LCP Budget

Performance budget calculator turns a target LCP and connection speed into a byte budget per asset type. See how much JS, CSS and image weight fits. Designed specifically for developers and professionals, this free online calculator runs entirely in your browser to process tasks quickly and securely. Enjoy unlimited usage with no data tracking and no registration required.

Also known as: performance budget calculator · web performance budget by page weight · lcp byte budget calculator · how much javascript can i ship · page weight budget calculator online · core web vitals budget planner · front end performance budget tool · calculate page size budget for lcp

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Target and Network

2500 ms LCP

Network profile

Target LCP (ms)

Bandwidth (Mbps)

RTT (ms)

Round trips

Server time (ms)

Round trips covers DNS, TCP and the TLS handshake before the first byte arrives. Four is a reasonable default for a cold HTTPS connection. Profiles are editable starting points, not vendor presets.

Byte Budget

Your total page weight budget and per-asset split will appear here.

About Performance Budget Calculator

A performance budget is the answer to how many bytes you can ship and still hit a target LCP on a given connection. Most teams set the target and never convert it into a number a developer can act on, so the budget gets argued about instead of enforced. This does the arithmetic: subtract latency from your target, multiply the time left by the throughput, and split the result across asset types.

Key Features

Converts a target LCP and connection speed into a total byte budget
Subtracts DNS, TCP and TLS round trips before counting transfer time
Accounts for server think time separately, so backend cost is visible
Splits the budget across HTML, CSS, JavaScript, images and fonts
Tells you when latency alone has already spent the whole budget
Recalculates live as you change any input, with every assumption on screen

Use Cases

Set a page weight budget before a redesign rather than arguing after it
Show why a 300 KB JavaScript bundle cannot hit a 2.5 second LCP on Slow 4G
Give a CI performance check a concrete byte threshold to fail on
Work out how much image weight is left after the framework is accounted for
Compare the budget on cable against a mobile connection for the same target
Demonstrate that cutting round trips buys more than compressing assets further

Supported Formats

Target LCP in ms

Bandwidth in Mbps

RTT in ms

Transferred bytes

Related Keywords

performance budget calculator

web performance budget by page weight

lcp byte budget calculator

how much javascript can i ship

page weight budget calculator online

core web vitals budget planner

front end performance budget tool

calculate page size budget for lcp

Why does my budget shrink so fast when latency goes up?

Because latency is spent before a single byte of payload moves. A cold HTTPS connection costs roughly four round trips for DNS, TCP and TLS, so at 150 ms RTT you have burned 600 ms before the server even starts thinking. Add 200 ms of server time to a 2,500 ms target and only 1,700 ms is left to actually transfer anything. That is why shaving round trips, through HTTP/2 or 3, connection reuse, preconnect hints and fewer origins, often buys more headroom than another round of asset compression. Note the result is transferred bytes, so compare it against the Transferred column in DevTools rather than the uncompressed resource size.

Privacy & Security

All processing happens locally in your browser. Your data never leaves your computer, ensuring complete privacy and security.

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Frequently asked questions

What is Performance Budget Calculator used for?

Performance budget calculator turns a target LCP and connection speed into a byte budget per asset type. See how much JS, CSS and image weight fits.

Is Performance Budget Calculator free to use?

Yes. Performance Budget Calculator is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use Performance Budget Calculator?

No. Performance Budget Calculator works immediately in your browser with no signup, login, or email address required.

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