Guideline

While there is no standard assumed for the connection speed of target users, it is current practice to keep file sizes as low as possible to allow for reasonable download speeds.
It is recommended to keep the home page under 60 KB (including all associated elements) and other HTML pages under 100 KB.

Designing for low bandwidth

The following guidelines highlight how to make Web sites accessible to users with low bandwidth Internet connections:

• Reduce the number of images - use CSS for layout and rollover effects instead of images. Optimize images for the lowest acceptable level of quality to reduce file size. Ensure Web sites are usable if images are turned off in the browser.
• Provide clear and logical navigation. Don't make users load unnecessary pages.
• Put main navigation items at the top of each page so they load and display first to make pages useful before they finish downloading.
• Use style sheets (CSS) for page layout rather than tables. Avoid using JavaScript. Use external style sheets rather than embedding rules within the HTML page.
• Minimise HTTP requests. Every image, CSS file, JavaScript file and HTML page requires a separate HTTP request. Increasing the number of these requests will add delays to page loading.
• Allow browsers to keep a local copy, or 'cache' of you pages.
• Avoid PDFs. When used ensure they are optimised for the Web.
• Show link sizes. Users should be allowed to link to items rather than be forced to download large items. Show the size next to the link, e.g. PDF Report (237kb).

See the Adaptive Web site for more information on these Web Design Guidelines for Low Bandwith Users.

Download times

The timetable below gives you an idea of how long it takes to download a range of file sizes at various connection speeds.

 

Connection Speed	File Size
	100 KB	500 KB	1 MB	1.5 MB	2 MB	5 MB
9600 bps	1:25 minutes	7:07 minutes	14:13 minutes	21:20 minutes	28:27 minutes	71:07 minutes
(9.6 KBps)
14400 bps	57 seconds	4:44 minutes	9:29 minutes	14:13 minutes	18:58 minutes	47:24 minutes
(14.4 KBps)
28000 bps	28 seconds	2:22 minutes	4:44 minutes	7:07 minutes	9:29 minutes	23:42 minutes
(28.8 KBps)
33600 bps	24 seconds	2:02 minutes	4:04 minutes	6:06 minutes	8:08 minutes	20:19 minutes
(33.6 KBps)
56000 bps	15 seconds	1:13 minutes	2:27 minutes	3:39 minutes	4:53 minutes	12:11 minutes
(56 KBps)
128 KBps	6 seconds	32 seconds	1:4 minutes	1:36 minutes	2:08 minutes	5:20 minutes
(ISDN)
1.5 MBps	< 1 second	3 seconds	5 seconds	8 seconds	11 seconds	27 seconds
(T1)
45 MBps	< 1 second	< 1 second	< 1 second	< 1 second	< 1 second	< 1 second
(T3)