How to use this calculator
- Enter or choose data size.
- Enter or choose size unit.
- Enter or choose connection speed.
- Enter or choose speed unit.
- Enter or choose efficiency.
- The transfer time updates as you type. Use Copy result or Share to keep it.
Method
Time (s) = Size in bytes × 8 ÷ (Speed in bits per second × Efficiency%)
- 8
- bits per byte
- Speed
- kbps = 10³, Mbps = 10⁶, Gbps = 10⁹ bits per second; MB/s = 8 × 10⁶ bits per second
Worked example
- Size: 10 GB = 10 × 10⁹ bytes × 8 = 80 × 10⁹ bits.
- Effective speed: 100 Mbps × 90% = 90 × 10⁶ bits/s.
- Time: 80 × 10⁹ ÷ 90 × 10⁶ = 888.9 s ≈ 14 min 49 s.
A 10 GB file takes about 14 minutes 49 seconds on a 100 Mbps line at 90% efficiency (13 min 20 s at the full line rate).
What the result means
If a transfer of many terabytes takes days, shipping a physical disk or a provider’s offline transfer appliance may be faster. For backups, compare the result with your backup window.
Assumptions and limits
- The speed is sustained for the whole transfer.
- Very high-latency links can be limited by TCP window size rather than line rate; small files add per-file overhead.
Questions
What is the difference between Mbps and MB/s?
Mbps is megabits per second; MB/s is megabytes per second. 1 MB/s = 8 Mbps, so a 100 Mbps line delivers at most 12.5 MB/s.
Why does my 1 TB drive show as 931 GB?
The drive maker uses decimal TB (10¹² bytes); many operating systems show binary GiB (2³⁰ bytes) labelled “GB”. 10¹² ÷ 2³⁰ ≈ 931.