Simple Throughput Formula

To calculate throughput in megabits per second (Mbps), divide 8192 by the time it takes to copy a 1 gigabyte file (2^30 bytes, or 1,073,741,824).

v = 8,192 / t

v – Throughput in Mbps

t – Time in seconds, that it takes to copy a 1 gigabyte file

This simple throughput test allows you to quickly check actual throughput for storage or network connections, and can be a valuable troubleshooting tool.

Example:

A 1 gig file takes 300 seconds to copy.

8,192 / 300 = 27.3 Mbps (Megabits per second)

How does this work?

Throughput is the number of bits transferred, in a specified amount of time (in seconds).

File size is measured in bytes, while throughput is measured in bits per second.  As there are 8 bits in a byte, the first step is to multiply the file size by 8, to get the total number of bits.

If we have a 1 gig file, that’s 1,073,741,824 bytes, or 8,589,934,592 total bits to transfer.

If we divide at this point, we will get a really large number, representing “bits per second” (bps).

When dealing with network or internet throughput rates, we typically use a much larger scale, such as megabits per second.  A kilobit is 1024 bits, and a megabit is 1024 kilobits (or 1024 * 1024 bits).  To go from bits to megabits, we divide by 1024 * 1024 ( 1,048,576 ).

So for a given file size f, taking time t in seconds to copy, the throughput v is as follows:

v = ( f * 8 / ( 1024 * 1024 ) ) / t)

v = ( f * 8 ) / ( 1024^2 * t )

With a file size of 1 gigabyte (1024 * 1024 * 1024 bytes), the equation looks like this:

v = ( 1024^3 * 8 ) / ( 1024^2 * t )

Since 1024^3 / 1024^2 = 1024, the above can be simplified to:

v = ( 1024 * 8 ) / t

v = 8,192 / t

Variations

To specify throughput in Gbps (Gigabits per second), simply divide 8 by the time in seconds.  Since you would be dividing 8192 by 1024 to go from megabits to gigabits, the answer, 8 represents the original 1 gig (abyte) file converted to bits, which is simply 1 (the file size) times 8 (the number of bits in a byte).

v (Gbps) = 8 / t

The problem is that, as the time taken to copy the file approaches 1 second or less, you lose precision.

Let’s say your 1 gig file takes 0.9 seconds.  The throughput is 8 / 0.9 = 8.9 Gbps.  The problem is that measuring 9/10 of one second, which is 900 milliseconds, takes a sensitive and precise timer.

One way around this is to scale everything up – for example, using a 10 gig file means we simply multiply the number of gigabits by 10:

v (Gbps) = 80 / t

Now, our 10 gig file might take 9 seconds, a quantity of time we can easily count using a stopwatch, but yields the same result:  80 / 9 = 8.9 Gbps.

As storage and networking become faster, larger file sizes are required, to make an accurate measurement.

How Do I Create a 1 Gig File?

In Windows, use these commands at a command prompt:

echo ABCDEF>test.txt
for /L %i in (1,1,27) do type test.txt >> test.txt

The first line creates an 8 byte file.  6 bytes are in the string “ABCDEF”, followed by a Carriage Return and Line Feed, that you don’t see, are also stored in the file.

The second line counts from 1 to 27, and adds the file to the bottom of itself, doubling the file each time.

Since the original file is 2^3 bytes, if we double it, the resulting file is 2^4 bytes.  If we double it 27 times, the file size is 2^(3 + 27), or 2^30, which is exactly 1 gig.