Data transfer time – How can I calculate how long it will take to transfer a file over LAN?

If I am sending a 1 GB file through a 1 Gb/s LAN connection, from one computer to another, how much time will it take to transfer that file?

In a 1 Gbps connection, 1 Gigabit will take 1 second. Since there are 8 bits in a byte, 1 Gigabyte will take 8 times longer.

So your 1 GB file will take 8 seconds in ideal conditions. However, hard disk speeds are usually much slower, so your file transfer might take three times longer to complete.


take to copy a 2TB file over the WAN, and I have to figure out how many Mb/sec that all translates to.  It’s not all that difficult, but it’s kind of a pain.  For example, if it took 32 hours to transfer 3TB, that’s:

(3tb * 1024 gb* 1024 mb* 8speed wan) / (32 * 60 * 60) =  218.45 Mb/sec

in the example above, the data was transferred over a 1 Gb/sec link, but the actual throughput was only 218 Mb/sec (0.213 Gb/sec or 21.3% efficiency).

From experience, I know USB 2.0 copies about 10Mb/sec on average (on my system).

So that would be
1TB == 1048576 Mb
1048576 / 10 ==> +/- 104857 secs
104857 / 60 ==> +/- 1747 mins
1747 / 60 ==> +/- 29 hours

So a full day and 5 hours.



Note that: The 1GB file = 1 x 2^30 bytes = 2^33 bits. (on Windows OS as it incorrectly uses SI prefix when they should be using IEC instead.. [1])

While the data transfer rate: 1Gb/s = 10^9bps.[2]

So “ideally” it would take…

2^33 bits / 10^9bps = (8,589,934,592)b / (10^9)bps = ~8.58s

Ofcourse, the HDD latency, network parameters, propagation delay, etc.. play a part in the final estimation.

This means 1Gigabit = 0.125 GigaBytes = 125 MegaBytes.This means the theoretical maximum of a 1Gbps connection is 0.125 GigaBytes per second.

Remember, the entire connection will run at the speed of the slowest element. So, if you’re downloading to your hard drive you’d expect it to be limited to the speed of the drives – about 60-70MB/s for a common mechanical hard drive.

Chances are even if there’s nothing else to limit the speed you will still not achieve the theoretical maximum speed for data transfer because of other restricting factors such as packet overhead.

Also, you ideally want to make sure you are using Cat6 cabling, not Cat5/5e

Note on size prefixes

This section is why I felt I’d add my answer, even though it’s a moderate dupe of the answers so far.

There are two main schemes for prefixing bytes to indicate magitude:

SI Prefix (abbr)= Num Bytes             |  IEC Prefix (abbr)= Num Bytes       
1 GigaByte (GB) = 1 000 000 000 (10^9)  |  1 GibiByte (GiB) = 1 073 741 824 (2^30)
1 MegaByte (MB) = 1 000 000     (10^6)  |  1 MebiByte (MiB) = 1 048 576     (2^20)
1 KiloByte (KB) = 1 000         (10^3)  |  1 KibiByte (KiB) = 1 024         (2^10)

It is highly common for most people to use the SI prefix to mean the IEC number of bytes, although in all “offical” terms this usage is deprecated and shouldn’t be used. It doesn’t help that both prefix patterns are often incorrectly represented by the same short versions – you often can’t tell just by looking if GB is GigaByte or GibiByte, even though it should be Giga, it’s often used to represent Gibi – such as in Windows Explorer for example.

This is why you often buy a 500GB hard drive that, when connected, only has ~465GiB of space – the manufacturer is using Giga, and the OS is using Gibi.



In terms of GigaBit Ethernet, it runs at a speed of 1000 Megabits per second – or 1 000 000 000 bits/s – so for completeness the final results are:

1 Gigabit  =  125 000 000 Bytes  =   125 MegaBytes  =   0.125 GigaBytes 
                                 =  ~119 MebiBytes  =  ~0.116 Gibibytes  
Amount of data:
Transfer rate:

Transfer time:


Note that transfer rates are quoted as binary values (i.e. 1 Mbps = 1024 Kbps). Also note the difference between the case of the “b” – “-bps” means bits per second and “-Bps” means Bytes per second.

For data quantity, you may choose between binary (e.g. MiB) or decimal (e.g. MB) versions of units.
For reference, typical modem speed is 56 kbps and broadband connection may range from 128 kbps to 25 Mbps (although it is normally in the 1-5 Mbps range).