Data Transfer Time Calculator

Estimate how long a migration, backup seed or bulk copy will take on your link, or how fast a link you need to meet a deadline.

Inputs

Result

Enter the amount of data and the link speed to see the transfer time.

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How the calculation works

Transfer time = data in bits ÷ effective throughput.

Data in bits = size in bytes × 8.
Effective throughput = link speed × efficiency.

Speed needed for a deadline = data in bits ÷ (deadline in seconds × efficiency). The result is the link speed to buy or provision; the data rate itself is the link speed times the efficiency.

Units. Decimal sizes use powers of 1,000: 1 MB = 10⁶ bytes, 1 GB = 10⁹, 1 TB = 10¹². Binary sizes use powers of 1,024: 1 MiB = 2²⁰ bytes, 1 GiB = 2³⁰, 1 TiB = 2⁴⁰. Link speeds are always decimal: 1 Mbps = 10⁶ bits per second and 1 Gbps = 10⁹.

Efficiency is the share of the link speed that carries your data. On standard Ethernet with a 1,500-byte MTU, each full frame carries 1,460 bytes of TCP payload in 1,538 bytes of wire time (headers, preamble and the gap between frames), so headers alone cost about 5%. The 90% default is a planning assumption that leaves a little room for the rest. A long-distance link with one TCP stream, packet loss, VPN encryption, slow disks or a link shared with daytime traffic can be far below that. The best number is a measured one: time a test copy of a few gigabytes and divide.

The result assumes the link is yours for the whole transfer at a steady rate. It does not include the time to read, compress, deduplicate or verify the data.

Worked example

10 TB over 1 Gbps. At 90% efficiency the effective throughput is 900 Mbps (112.5 MB/s):

10 TB = 10 × 10¹² bytes × 8 = 8 × 10¹³ bits
8 × 10¹³ ÷ 900,000,000 bits per second = 88,889 seconds = 24.69 hours, about 1 day 41 min

If the 10 came from Windows and is really 10 TiB, the data is 10 × 2⁴⁰ bytes, about 10% more, and the same link takes 97,734 seconds, about 1 day 3 h 9 min (27.15 hours).

50 TB in 7 days. To finish a 50 TB migration within a week at 90% efficiency:

50 TB × 8 = 4 × 10¹⁴ bits
7 days = 604,800 seconds
4 × 10¹⁴ ÷ (604,800 × 0.9) = 734.9 Mbps of link speed, moving data at 661.4 Mbps (82.67 MB/s)

A 1 Gbps circuit would do it using about 73% of its capacity; a 500 Mbps circuit would not.

Frequently Asked Questions

How long does it take to transfer 1 TB over a 1 Gbps link?

At the full line rate, 1 TB (10^12 bytes) is 8 × 10^12 bits, which takes 8,000 seconds, or 2 hours 13 minutes 20 seconds. At 90% efficiency it takes about 2 hours 28 minutes. Over 100 Mbps the same terabyte takes ten times as long: about 24 hours 41 minutes at 90%.

What is the difference between TB and TiB?

A terabyte (TB) is 10^12 bytes; a tebibyte (TiB) is 2^40 bytes, about 1.0995 × 10^12, so 10% more data. Drive makers quote decimal TB, while Windows reports binary sizes but labels them TB. If your size came from Windows Explorer, choose TiB, GiB or MiB.

Why is a transfer slower than the link speed?

Link speed counts every bit on the wire, including Ethernet, IP and TCP headers, so even a perfect transfer delivers about 95% of the line rate as file data on a standard 1,500-byte MTU. Beyond that, a single TCP stream over a long distance can be limited by latency and window size, packet loss forces resends, and encryption, the storage at either end or a shared link can each be the bottleneck.

Are Mbps and MBps the same?

No. Mbps is megabits per second and MB/s is megabytes per second; one byte is eight bits. A 1 Gbps link moves at most 125 MB/s. Network speeds are quoted in bits and file sizes in bytes, which is why the calculator multiplies the size by 8.

When is shipping a drive faster than the network?

When the transfer time is longer than it takes to copy the data to a device, ship it and load it at the other end. Cloud providers offer import services for this. Use the speed-needed option with your deadline: if the link it asks for is far above what you have or can buy in time, plan for a device or a temporary faster circuit.