There's a wide variety of connection speeds in use; look to your core audience to see what their typical connection is.
Bandwidth is measured in bits of data transmitted per second. Higher bandwidth connections include:
- T-3, which moves data at 45 megabits per second (45,000,000 bits per second)
- T-1, which moves 1.544 megabits per second (1,544,000 bits per second)
- DSL, which moves data between 384 kilobits (384,000 bits) and 1.5 megabits per second
- Cable modem, which moves data at 1.5 megabits per second
Lower bandwidth connections are typically made through a modem. Three common modem speeds are:
- A 56k modem, which moves 56,000 bits-per-second
- A 28.8K modem, which moves 28,800 bits per second
- A 14.4K modem, which moves 14,400 bits per second
Always take connection speed with a grain of salt. Just because a 56K modem is capable of delivering 56,000 bits per second doesn't mean it actually will. Phone line quality, number of users, distance from the main pipeline, volume of data, speed and reaction time of your server, general web traffic, and other factors slow down even the higher bandwidth connections.
Consider your audience's reality as you make your design decisions. If they are all on DSL you have more leeway than if they connected via 28K or 56K modems. For modem connections, 1K=1second is a good general guideline. On DSL, cable modems and other faster connections, use 5K=1 second as your guide.
Remember to add all elements on page when you calculate page size. HTML uses bandwidth, too.