Bandwidth and Transfer Time Calculator

Three calculations with the same relationship

A transfer relates the amount of data, the rate and the time. This calculator allows you to enter two of these magnitudes to obtain the third:

• Transfer time: how long an amount of data would take at a constant rate.
• Required bandwidth: what nominal rate would allow the transfer to be completed in the target time.
• Transferable data: how much could be sent during a specific interval.

The result is a mathematical estimate. The tool does not download a test file, measure your connection or promise the speed a real network will achieve.

Verifiable examples

10 GB at 100 Mbit/s

Ten decimal gigabytes contain 80,000,000,000 bit. At a constant rate of 100,000,000 bit/s and an efficiency of 100%, the time is:

80,000,000,000 bit ÷ 100,000,000 bit/s = 800 s
800 s = 13 min 20 s

The same nominal rate is equivalent to 12.5 MB/s or approximately 11.920929 MiB/s.

50 GiB in 30 minutes

If you want to transfer 50 GiB into 30 min with an estimated efficiency of 90%, the minimum nominal rate is approximately 265.121438 Mbit/s. The rate effective target for useful data would be 238.609294 Mbit/s.

1 Gbit/s for 2 hours

A nominal rate of 1 Gbit/s during 2 h, with an efficiency of 80%, allows you to transfer 720 GB, equivalent to about 670.552254 GiB.

Formulas used

The calculator first normalizes the data to bits, the rate to bits per second, the time to seconds and the efficiency to a number between 0 and 1:

D = data in bits
R = nominal rate in bits per second
E = efficiency
T = time in seconds

Effective rate:      Re = R × E
Transfer time:       T = D ÷ (R × E)
Required bandwidth: R = D ÷ (T × E)
Transferable data:  D = R × E × T

These formulas assume a constant rate. Latency, congestion, losses, broadcasts, server limits, Wi-Fi and other factors may change the observed result.

Mbps is not the same as MB/s

The lowercase b represents bits and the uppercase B represents bytes. One byte contains eight bits, so:

100 Mbit/s ÷ 8 = 12.5 MB/s
600 Mbit/s ÷ 8 = 75 MB/s

The interface uses Mbit/s and MB/s to make the difference clear. Avoid the ambiguous form MBps.

The guide Mbps and MB/s: differences and transfer time explains how to keep units throughout the calculation and when to distinguish MB from MiB.

Decimal and binary units

Decimal prefixes advance in powers of 1,000:

1 kbit = 1,000 bit
1 Mbit = 1,000,000 bit
1 kB   = 1,000 B
1 MB   = 1,000,000 B
1 GB   = 1,000,000,000 B

Binary prefixes advance in powers of 1,024:

1 KiB = 1,024 B
1 MiB = 1,048,576 B
1 GiB = 1,073,741,824 B

That’s why 1 GB and 1 GiB are not the same quantity. NIST collects both the decimal SI prefixes and IEC binary prefixes.

To convert a capacity without adding time or speed, use the storage unit converter. The guide GB and GiB: differences and how to convert them explains the two scales with examples of disks and memory.

How to use efficiency

The initial value is 100%, which shows the ideal duration at the full nominal rate available for the calculated data. You can enter a lower percentage to model your own estimate.

There is no universal overhead percentage. RFC 5166 distinguishes throughput and goodput, which may differ because of losses, retransmissions and traffic that is not useful data. RFC 6349 also describes how RTT, the TCP window and other conditions affect performance. For this reason, the tool never applies an automatic “10% TCP/IP overhead”.

Common errors

• Enter numbers greater than zero; negative values are not allowed.
• You can use 1,5 or 1.5, but do not mix commas and periods.
• Do not use thousands separators: write 1000, not 1,000.
• Exponents such as 1e6, NaN or infinity are not supported.
• The efficiency must be greater than 0 and less than or equal to 100.
• Check whether the size is expressed in bits, decimal bytes or binary bytes.
• Check if your provider expresses the rate in Mbit/s and not in MB/s.

Each entry is limited to 10^15 in the selected unit and 64 characters. If a combination does not produce a finite number, the calculator displays an error instead of presenting Infinity or NaN.

Estimation limits

This version does not perform a speed test or recommend connectivity plans or video presets. It also does not calculate the bandwidth-delay product, TCP windows, user concurrency or protocol overhead. Those questions require different inputs and explanations.

RFC 5136 warns that “Bandwidth” is often used synonymously with capacity although the terms are not technically identical. Here it represents the nominal rate entered or the minimum calculated rate, always in bits per second before displaying its equivalences.

Frequently asked questions

Does the calculator measure my actual speed?

No. It only combines the values you enter. It does not generate network traffic or connect to a measurement server.

What efficiency should I set?

Use 100% for the ideal mathematical case. Enter another percentage only if you have your own estimate or want to compare scenarios. The tool does not recommend a universal value.

Is it useful for uploads, copies and backups?

Yes. The relationship between data, rate and time is the same. The result remains an estimate if the rate changes during the operation.

Why does it show GB and GiB at the same time?

Because they are different units. Showing both avoids interpreting a quantity decimal as if it were binary, or the other way around.

Are the entered values saved?

No. The calculation happens in this tab. The values and results disappear when you reload or close the page.