Bandwidth is the maximum data rate of your connection, quoted in megabits per second (Mbps) or gigabits per second (Gbps) — and it is the number that decides what your household or office can do simultaneously. The planning method is additive: list the concurrent activities, assign each a typical bitrate, sum them, and add headroom. Reference bitrates: 4K streaming 15-25 Mbps, HD streaming 5-8 Mbps, video calls 2-10 Mbps (group calls higher), online gaming 5-25 Mbps (latency matters more than speed), music streaming under 1 Mbps, general browsing 1-5 Mbps per active user.
The headroom rule: provision about 25 to 50 percent above the computed sum, because usage peaks, background updates, and cloud backups all strike at once. A household summing to 70 Mbps of concurrent use should buy a 100 Mbps plan, not a 75 Mbps one. Also distinguish download from upload: video conferencing, cloud backup, and content creation are upload-hungry, and many cable plans offer uploads at one-tenth the download speed — a '200 Mbps' plan with 10 Mbps up will choke on two simultaneous video calls.
Advertised speeds are 'up to' figures; measure what you actually get with a speed test at peak hours, wired if possible. If measured speed is far below the plan, the bottleneck is usually Wi-Fi coverage or an aging router, not the ISP — fix the local network before paying for a bigger plan. This calculator sums your usage profile into a recommended plan size.