Bandwidth & Transfer Time Calculator
How long will that file take? Convert between bps, MB/s, and time-to-transfer with realistic efficiency factor.
Why your "100 Mbps" connection moves at 12 MB/s
Internet speeds are sold in bits per second. File sizes are in bytes. One byte = 8 bits. So 100 Mbps ≈ 12.5 MB/s in theory, ~10–11 MB/s in practice after TCP overhead, retransmits, and the gentle dishonesty of marketing.
| Connection | Theoretical max | Real-world |
|---|---|---|
| 10 Mbps DSL | 1.25 MB/s | ~1.0 MB/s |
| 100 Mbps cable | 12.5 MB/s | ~10–11 MB/s |
| Gigabit fiber | 125 MB/s | ~100–115 MB/s (TCP/Ethernet limits) |
| 10 Gbps | 1.25 GB/s | Often CPU-limited at the endpoints |
The "efficiency" slider on the calculator above lets you set realistic expectations. Defaults to 85%, which is reasonable for direct wired transfers; drop to 50–65% for typical home WiFi.