Mbps vs MB/s: the 8× confusion
Internet speeds are sold in megabits per second (Mbps, small “b”). Browsers, Steam and file managers show downloads in megabytes per second (MB/s, big “B”). There are 8 bits in a byte, so:
100 Mbps ÷ 8 = 12.5 MB/s 1 Gbps ÷ 8 = 125 MB/sThat’s why a “100 Mbps” connection never shows 100 in your download bar. It isn’t slow. It’s just a different unit.
MB vs MiB: why Windows shows smaller numbers
Storage makers and networking use decimal units (1 GB = 1,000,000,000 bytes). Windows and many tools use binary units but still label them “GB” (1 GiB = 1,073,741,824 bytes, about 7.4% more). A “1 TB” drive shows as about 931 GB in Windows. Pick the unit your file size came from: choose GiB/MiB if the number is from Windows Explorer.
Why real transfers are slower than the maths
- Protocol overhead: TCP/IP headers, TLS encryption and Ethernet framing use roughly 5–10% of the line rate. Wi-Fi and VPNs can use 20–40%.
- Latency and TCP windows: a single download over a long-distance, high-latency link often can’t fill a fast pipe. Multi-threaded tools help.
- The slowest link wins: your disk, the remote server, Wi-Fi signal or a congested ISP peering point can all be the bottleneck.
- Asymmetric plans: many broadband plans upload far slower than they download. Use your upload speed for backups to the cloud.
Rule of thumb: at 100 Mbps you move about 45 GB per hour in theory, or roughly 40 GB per hour after 10% overhead. At 1 Gbps it’s about 400 GB per hour.