Page Weight Budget Calculator
Set a performance budget for your web page from a target load time and connection speed, then check whether your current asset sizes fit inside it.
How it works
Usable s = target × (1 − overhead%) · Budget MB = speed Mbps × 1e6 ÷ 8 × usable s ÷ 1024²
A performance budget turns a load-time goal into a hard byte ceiling. Take your target time, subtract the share eaten by connection setup and round-trips before real data flows, and multiply the remaining seconds by throughput to get the bytes you can afford. Because Mbps counts megabits, divide by 8 for bytes. Budgeting against a cautious mobile speed rather than your office fibre is what keeps pages fast for the visitors most likely to bounce.
Worked example
Aiming for 3 s over 5 Mbps, reserve 20% (0.6 s) for latency, leaving 2.4 s. That carries 5 × 1,000,000 ÷ 8 × 2.4 = 1,500,000 bytes ≈ 1.43 MB. A 2.5 MB page is about 1.07 MB over budget and needs trimming.
Frequently asked questions
Why reserve time for overhead?
Before any page bytes arrive, the browser spends time on DNS, the TCP/TLS handshake and the first server round-trip — often several hundred milliseconds on mobile. Reserving 15–25% of the budget for that keeps the estimate honest; raise it for pages with many third-party connections.
What speed should I budget against?
Pick a speed near the slow end of your real audience, not the median. A common choice is a throttled 4G profile around 5 Mbps, which protects visitors on congested or rural networks who are the first to abandon a heavy page.
Does compression count?
The budget is about bytes transferred over the wire, so use the compressed (gzip/brotli) transfer size that your dev tools report, not the uncompressed source size. Enabling text compression is one of the cheapest ways to fit the budget.
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This calculator is for educational purposes. Double-check important results before acting on them.