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Web metrics: Size and number of resources

Author: Sreeram Ramachandran, Software Engineer
Last updated: 26 May 2010

Here are some statistics about the size, number of resources and other such metrics of pages on the world wide web. These are collected from a sample of several billions of pages that are processed as part of Google's crawl and indexing pipeline. In processing these pages, we not only take into account the main HTML of the page, but also discover and process all embedded resources such as images, scripts and stylesheets.

Highlights:

The average web page takes up 320 KB on the wire.
Only two-thirds of the compressible material on a page is actually compressed.
In 80% of pages, 10 or more resources are loaded from a single host.
The most popular sites could eliminate more than 8 HTTP requests per page if they combined all scripts on the same host into one and all stylesheets on the same host into one.

Caveats:

All resources are fetched using Googlebot, which means they are subject to robots.txt restrictions. For example, some sites (such as the BBC) block CSS and JS.
Some sites may present a different view of the resources to Googlebot than to regular users. For example, until recently, Google's own servers used to serve CSS and JS uncompressed to Googlebot, while compressing them for regular user browsers.
Pages are rendered and subresources are discovered through the eye of WebKit. If a page serves resources differently for Internet Explorer or Firefox, those won't be visible here.
Sampling of pages for processing is not uniformly random or unbiased. For example, pages with higher PageRank are more likely to be included in these metrics.

Averages:

Metric	Top Sites	All Sites	Description
Pages	380 million	4.2 billion	Number of sample pages analyzed.
Resources	42.14	43.91	Average number of resources per page.
GETs	42.63	44.56	Average number of GETs per page. Similar to number of resources, but also includes redirects.
Hosts	8.39	7.01	Average number of unique hostnames encountered per page.
Resources Per Host	5.02	6.26	Average number of resources per host (derived from the 'Resources' and 'Hosts' values).

Network Size/KB	312.04	320.24	Average size transferred over the network per page, including HTTP headers. If resources were compressed, this would use the compressed size.
Document Size/KB	477.26	376.67	Average uncompressed size of a page and its resources, excluding HTTP headers.
Zippable Size/KB	287.51	170.16	Average uncompressed size of the compressible resources on a page, i.e., those with a Content-Type of 'text/*' or equivalent.
Unzipped Size/KB	32.67	57.07	Average size of the compressible resources that were not sent compressed, i.e., the Content-Type was 'text/*', but Content-Encoding did not include 'gzip' or 'deflate'.
Zipped Ratio	89%	66%	Average percentage of compressible bytes that were actually compressed (derived from the 'Zippable' and 'Unzipped' values).

Images	27.58	29.39	Average number of unique images per page.
Image Size/KB	184.73	205.99	Average network size of the images per page.
Scripts	6.75	7.09	Average number of external scripts per page.
Script Size/KB	66.48	57.98	Average network size of the external scripts per page.
Combinable Scripts	4.75	3.75	Average number of requests that could be saved per page if external scripts on the same host were combined.
Stylesheets	4.07	3.22	Average number of external stylesheets per page.
Stylesheet Size/KB	27.17	18.72	Average network size of the external stylesheets per page.
Combinable Stylesheets	3.54	2.02	Average number of requests that could be saved per page if external stylesheets on the same host were combined.

SSL Pages	650 thousand	17 million	Number of sample SSL (HTTPS) pages analyzed.
SSL Hosts	6.39	3.23	Average number of unique hostnames encountered per SSL page.
SSL Zippable/KB	263.58	160.47	Average size of the compressible resources per SSL page.
SSL Unzipped/KB	133.74	89.36	Average size of the compressible resources that were not sent compressed, per SSL page.
SSL Zipped Ratio	49%	44%	Average percentage of compressible bytes that were actually compressed, per SSL page (derived from the 'SSL Zippable' and 'SSL Unzipped' values).

Percentiles:

Metric	Tier	Mean	Min	10	20	30	40	Median	60	70	80	90	Max
GETs Per Page	Top Sites	42.63	1	17	21	25	28	33	39	48	60	81	977
GETs Per Page	All Sites	44.56	1	10	18	24	30	37	45	54	66	86	2,758

Hosts Per Page	Top Sites	8.39	1	3	3	4	4	7	8	10	12	17	222
Hosts Per Page	All Sites	7.01	1	1	2	3	4	5	7	8	10	14	374

KB Per Page	Top Sites	312.04	0.00	38.15	80.44	119.28	145.51	176.23	208.38	275.48	377.16	597.08	312,426.25
KB Per Page	All Sites	320.24	0.00	21.82	54.15	90.76	131.30	177.47	234.67	310.51	428.73	663.19	517,026.13

KB Per Host	Top Sites	37.18	0.00	0.73	1.76	3.92	6.73	11.18	17.12	26.75	55.45	132.76	311,872.59
KB Per Host	All Sites	45.69	0.00	0.78	1.94	3.60	6.96	13.09	23.97	44.12	85.15	179.08	441,631.71

KB Per GET	Top Sites	7.32	0.00	0.46	0.68	1.06	1.60	2.36	3.19	4.76	7.76	16.75	14,852.58
KB Per GET	All Sites	7.19	0.00	0.43	0.63	0.92	1.31	1.93	2.90	4.38	7.96	18.46	35,932.92

GETs Per Host	Top Sites	5.08	1.00	2.11	2.88	3.50	4.50	5.62	6.75	8.00	9.20	11.25	401.00
GETs Per Host	All Sites	6.36	1.00	2.33	3.29	4.20	5.14	6.25	7.60	9.33	12.08	18.00	1,045.00

Max GETs Per Host	Top Sites	-	1	5	9	12	15	18	21	26	33	39	860
Max GETs Per Host	All Sites	-	1	6	10	15	19	24	29	36	44	59	2,754

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