Bits on the wire. Bytes on the drive.
Networks usually quote megabits per second (Mbps). File sizes use bytes, and each byte contains eight bits. Time in seconds equals data bytes × 8 ÷ (Mbps × 1,000,000 × utilization). Effective throughput in decimal MB/s is Mbps × utilization ÷ 8.
At 1,000 Mbps and 80% utilization, 1 TB takes about 2 hours 46 minutes 40 seconds. At a full 1,000 Mbps it takes 2 hours 13 minutes 20 seconds. A TiB is larger than a TB, so it takes longer at the same speed.
What utilization should I use?
Measure a representative transfer and compare it with line rate. A 1 Gbps connection carrying 100 MB/s is using 80% of its nominal capacity. Enter a conservative value when planning a deadline; no single utilization percentage fits every system.
Does this include incremental backups?
Enter the amount actually transferred, not the total protected dataset. Deduplication and compression can reduce that amount. Verification and restore testing may require additional time.
Before upgrading the network
Check the NIC, switch, cables, protocol and disk speeds together. A faster switch cannot fix a slow source disk. Use this estimate to compare scenarios, then benchmark your actual backup path.
Compare with the Calculator.net bandwidth calculator for additional bandwidth conversions.