Bandwidth is always measured in bits per second (bps) and its SI multiples: kilobits (kbps), megabits (Mbps), gigabits (Gbps). File transfer speeds, on the other hand, are displayed in bytes per second (KB/s, MB/s, GB/s). Because 1 byte = 8 bits, the two scales differ by a factor of 8 — which is why a "100 Mbps" internet connection downloads files at about 12.5 MB/s, not 100 MB/s.
The formula
1 byte = 8 bits (exact)
All bandwidth prefixes use SI (powers of 1000 — ISO/IEC 80000-13):
1 kbps = 1,000 bits/s
1 Mbps = 1,000,000 bits/s
1 Gbps = 1,000,000,000 bits/s
1 KB/s = 8,000 bits/s (8 × 1,000)
1 MB/s = 8,000,000 bits/s (8 × 1,000,000)
1 GB/s = 8,000,000,000 bits/s
Mbps → MB/s: divide by 8
MB/s → Mbps: multiply by 8
Note: bandwidth uses only SI prefixes. There is no "binary" version — nobody measures bandwidth in mebibits per second.
Practical examples
Example 1 — ISP plan vs download speed. You subscribe to 200 Mbps internet. Your download manager shows: 200 / 8 = 25 MB/s. A 10 GB file takes 10,000 / 25 = 400 seconds (~6.7 minutes) at full speed.
Example 2 — USB 3.0 transfer rate. USB 3.0 is rated at 5 Gbps. Practical throughput is ~400 MB/s: 5,000 / 8 = 625 MB/s theoretical maximum, minus overhead = ~400 MB/s real-world.
Example 3 — Server network interface. A 10 GbE (10 Gigabit Ethernet) card moves: 10,000 Mbps / 8 = 1,250 MB/s = 1.25 GB/s peak. Useful for calculating whether a link can sustain a backup job.
Common mistakes
- Interpreting ISP speeds as MB/s. The most common source of confusion. "500 Mbps fibre" = 62.5 MB/s download, not 500 MB/s. If a download seems slow, check whether your speed-test app displays Mbps or MB/s.
- Confusing network bandwidth with storage bandwidth. RAM bandwidth (e.g., "51.2 GB/s" for DDR5) uses binary GiB/s internally — but is marketed in SI GB/s. NVMe SSDs may quote "7 GB/s" in SI. These are not the same scale as network Gbps even though the notation looks similar.
- Assuming all bandwidth is usable throughput. TCP overhead, protocol headers, retransmissions, and half-duplex constraints reduce practical throughput to 85–95% of the rated link speed under ideal conditions.
International and regional variations
| Unit | Type | Value in bits/s | Common context |
|---|---|---|---|
| bps | bits/s | 1 | Modem specs, serial communications |
| kbps | bits/s | 1,000 | Audio streaming (MP3: 128–320 kbps) |
| Mbps | bits/s | 1,000,000 | ISP plans, Wi-Fi speeds, video streaming |
| Gbps | bits/s | 1,000,000,000 | Ethernet links, data center networking |
| KB/s | bytes/s | 8,000 | Small file transfers, serial port throughput |
| MB/s | bytes/s | 8,000,000 | Download managers, SSD benchmarks |
| GB/s | bytes/s | 8,000,000,000 | RAM bandwidth, NVMe SSD ratings |
Quick reference
| Mbps | MB/s | Gbps | GB/s |
|---|---|---|---|
| 10 | 1.25 | 0.01 | 0.00125 |
| 50 | 6.25 | 0.05 | 0.00625 |
| 100 | 12.5 | 0.1 | 0.0125 |
| 500 | 62.5 | 0.5 | 0.0625 |
| 1000 | 125 | 1 | 0.125 |
| 10000 | 1250 | 10 | 1.25 |