Page Load Budget Calculator
Whether a page fits its load-time target — bytes over the connection, plus round trips, against the budget you set.
Load time is transfer time plus latency.
How the page load budget calculator works
Load time is transfer time plus latency. Transfer is bytes over bandwidth; latency is round trips times RTT, and on a slow connection the round trips often cost more than the bytes.
That is why reducing requests matters as much as reducing size. Ten requests at 150 ms RTT is 1.5 seconds before a single byte of the last one arrives, regardless of how small it is.
Formula: time = bytes / bandwidth + round trips × RTT
Worked examples
| Inputs | Estimated load time | Note |
|---|---|---|
| 1.8 MB over 45 requests | 2.4 | over a 3 s budget |
| Fewer requests | 1.68 | latency collapses |
| A lighter page | 1.36 | comfortably inside |
FAQFrequently asked questions
What page weight should I aim for?
Under 1 MB is a reasonable target and under 500 KB is good. The right number depends on the connection your users actually have.
Why do requests matter as much as bytes?
Because each round trip costs the full latency regardless of size. On a 150 ms connection, twenty serialised requests cost three seconds before any of them transfers.
What is a realistic connection to test on?
Slower than yours. A 4G connection at 10 Mbps and 120 ms RTT is a fair mid-range target; many users have worse.
Does HTTP/2 fix the request cost?
It multiplexes over one connection, which removes the connection setup but not the latency of the dependency chain. Fewer, larger requests still win.
Is this the same as a Core Web Vitals score?
No. This is a transfer estimate; Core Web Vitals measure rendering and interactivity, which depend on what the browser does with the bytes.
Where these figures come from
- IEC 80000-13 — Information science and technology (quantities and units) — the decimal (kB, MB) versus binary (KiB, MiB) prefixes used throughout
- RFC 4632 — Classless Inter-domain Routing (CIDR) — the address-plan arithmetic behind the subnet calculator
- RFC 1918 — Address Allocation for Private Internets — the private ranges the subnet calculator recognises
- NIST SP 800-63B — Digital Identity Guidelines, Authentication — length over composition rules; the basis of the password guidance here
- NIST SP 800-57 Part 1 — Recommendation for Key Management — key-strength comparisons used by the key-space calculator
- National Cyber Security Centre — password guidance — UK national guidance on password policy
Last checked: September 2026. Units follow the SI decimal convention (IEC 80000-13 defines the binary alternatives); network and security figures cite the defining standard.