Why your 100 Mbps internet downloads at 12.5 MB/s, not 100
A plan advertised as "100 Mbps" never shows "100" in a download manager. That's not a slow connection — it's two different units describing the same link. ISPs quote bits per second (Mbps); operating systems and browsers report bytes per second (MB/s). There are 8 bits in a byte, so the two numbers are always off by a factor of 8.
The method
bytes per second = bits per second ÷ 8, and the reverse, bits per second = bytes per second × 8. Everything else is just moving the decimal for the metric prefix: 1 Kbit/s = 1,000 bit/s, 1 Mbit/s = 1,000,000 bit/s, 1 Gbit/s = 1,000,000,000 bit/s, and the same thousands-based scaling for KB/s, MB/s and GB/s.
A real example: a 100 Mbps plan's real download speed
Convert Mbit/s to bit/s: 100 × 1,000,000 = 100,000,000 bit/s. Divide by 8 to get bytes per second: 100,000,000 ÷ 8 = 12,500,000 byte/s, which is 12,500,000 ÷ 1,000,000 = 12.5 MB/s. A "100 Mbps" plan tops out at about 12.5 MB/s in a download manager — that's the ceiling, not a fault.
A real example: how long a 2.5 GB file takes on a 25 Mbps connection
Convert the file to the same unit as the connection. 2.5 GB is 2.5 × 1,000 MB = 2,500 MB, and in bits that's 2,500 × 8 = 20,000 Mbit. At 25 Mbit/s: 20,000 ÷ 25 = 800 seconds, or 800 ÷ 60 = 13.33 minutes. A 2.5 GB download on a 25 Mbps line takes about 13.3 minutes under ideal, uninterrupted conditions.
A real example: converting a download manager's MB/s back to Mbps
A speed test shows a steady 45 MB/s and you want to know what that would be sold as. Multiply by 8 to get back to bits: 45 × 8 = 360 Mbit/s. So a sustained 45 MB/s transfer corresponds to roughly a 360 Mbps connection — useful for checking whether a line is actually delivering what it's rated for.
Why real-world speeds run below the math
The ÷8 conversion gives the theoretical ceiling, not what you'll actually see. Real throughput is reduced by network overhead (packet headers, protocol handshakes), Wi-Fi signal quality, server-side limits, and other devices sharing the same connection. Seeing 80–90% of the converted ceiling on a wired connection is normal; Wi-Fi commonly loses more.
Run your own numbers
The free Data Rate Converter converts between bit/s, Kbit/s, Mbit/s, Gbit/s, Byte/s, KB/s and MB/s instantly, entirely on your device.