Bandwidth Calculator

A lowercase b is bits and an uppercase B is bytes, and 1 byte equals 8 bits. So 100 Mbps (megabits per second) is 100 / 8 = 12.5 MB/s (megabytes per second). ISPs quote line speed in bits per second because that is how network hardware is specified; download managers and file transfer UIs show bytes per second because that is how file sizes are measured. The calculator converts in both directions automatically.

The calculator uses decimal SI prefixes: 1 kbps is 1,000 bps, 1 Mbps is 1,000,000 bps, and 1 GB/s is 1,000,000,000 B/s. Binary prefixes use distinct names such as KiB and GiB. Check the unit label on file-size tools because some interfaces still use KB or GB for binary values.

Divide the cap by the seconds in 30 days (2,592,000) to get a sustained byte rate, then multiply by 8 to get bits per second. A 1 TB (1,000,000 MB) cap works out to about 3.09 Mbps held flat 24/7. A 1.2 TB cap is about 3.7 Mbps sustained. That is why a single 4K stream at ~25 Mbps can hit a household cap inside a few hundred hours of viewing per month.

A 1 Gbps line is a nominal rate, not a guaranteed application-transfer rate. Protocol overhead, packet size, transport settings, congestion, storage, and the slowest link all affect throughput. Around 940 Mbps is common for large TCP transfers over ordinary gigabit Ethernet, but it is not a universal ceiling or discount factor.

Network rates are conventionally stated in bits per second, while file sizes and transfer interfaces often use bytes. Because 1 byte is 8 bits, 100 Mbps equals 12.5 MB/s before overhead. Convert both values to the same unit before comparing them.