Website Page Weight Load Time Calculator

Page weight is the total transferred byte count of every subresource a browser must fetch to render a page: the HTML document, stylesheets, scripts, images, web fonts, and miscellaneous assets such as JSON payloads and media. Converting that figure to a load time requires two separate terms. The bandwidth term divides the payload by throughput, and because file sizes are quoted in kilobytes while link rates are quoted in megabits per second, the conversion multiplies by 8 and divides by 1024. The latency term is independent of size: a TCP handshake costs one round trip, a TLS 1.2 negotiation costs two more (TLS 1.3 reduces this to one), and DNS resolution can add another. Under HTTP/1.1 a browser opens roughly six parallel connections per origin, so 60 subresources serialize into about ten latency-bound batches, whereas HTTP/2 multiplexes them over a single connection. The HTTP Archive median page has hovered between roughly 2.2 and 2.6 MB in recent years, with images typically over half the bytes and JavaScript the second largest share. Google treats a Largest Contentful Paint at or below 2.5 seconds as good and above 4.0 seconds as poor, with Cumulative Layout Shift at or below 0.1 and Interaction to Next Paint at or below 200 milliseconds. Any model of this kind is optimistic: it ignores TCP slow start, where an initial congestion window of about ten segments caps the first round trip near 14 KB, and it ignores the CPU cost of parsing and executing JavaScript, which on mid-range phones can exceed the download time itself.

Systematic measurement of page weight began with the performance engineering work of Steve Souders, whose 2007 book High Performance Web Sites codified the rules that Yahoo shipped as the YSlow browser extension in the same year. Souders went on to found the HTTP Archive in 2010 in partnership with the Internet Archive, creating the longitudinal dataset that made statements about the average page size possible; that dataset recorded the median page crossing 1 MB around 2014 and 2 MB by 2018. Google released its own PageSpeed tooling in 2010 and replaced it with Lighthouse in 2016. The transport-level ingredients arrived earlier. Gzip was specified in RFC 1952 in 1996 and adopted as an HTTP content coding, while Brotli, developed at Google and published as RFC 7932 in 2016, typically compresses text 15 to 25 percent better. HTTP/2 grew out of the SPDY protocol Google announced in 2009 and was standardized as RFC 7540 in 2015, eliminating the head-of-line blocking that had forced practices such as sprite sheets and domain sharding. Google announced Core Web Vitals in May 2020 and folded them into ranking as part of the 2021 page experience update, then replaced First Input Delay with Interaction to Next Paint in March 2024.