Computers & Laptops

Data Transfer Time Calculator

How long a transfer takes, with bits and bytes kept apart - 100 Mbps is 12.5 MB/s, not 100.

4 inputs Free, no sign-up

Your figures

From a benchmark, a previous transfer, or the interface's rating. Watch the units - a drive is usually quoted in MB/s and a network link in Mbps.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

100 Mbps is not 100 MB/s. It is 12.5 MB/s. A byte is eight bits, storage is measured in bytes and links are rated in bits, so every transfer estimate crosses that factor — and getting it wrong is the difference between two minutes and a quarter of an hour.

This page keeps them apart. The unit list says which family each rate belongs to, and the result shows your speed converted into the other one.

How to use this calculator

  1. Enter how much data you are moving.
  2. Enter the speed, and pick its unit carefully. The list names bits and bytes explicitly.

The formula

Time = Data in bytes / Speed in bytes per second

1 byte  = 8 bits
1 Mbps  = 125,000 bytes per second
1 MB/s  = 1,000,000 bytes per second
SymbolMeaningUnit
Data How much you are moving GB
Speed Sustained transfer rate MB/s or Mbps

Worked example

5 GB over a 100 Mbps link:

5 GB       = 5,000,000,000 bytes
100 Mbps   = 12,500,000 bytes per second
Time       = 400 seconds = 6 minutes 40 seconds

The same 5 GB at 100 MB/s — an ordinary SSD figure — takes 50 seconds.

Notes and limits

  • This assumes the speed is sustained for the whole transfer, which it rarely is. Protocol overhead, the device at the other end and a drive's own write cache all get in the way.
  • Copying many small files is much slower than one large file of the same total size, because each file costs a fixed amount of work regardless of its size.
  • A drive's advertised sequential speed is its best case. Sustained writes on an SSD drop sharply once the fast cache is full.
  • USB and Thunderbolt ratings are in bits: USB 3.0's "5 Gbps" is 625 MB/s before overhead, and real throughput is well below that.

What this calculation assumes

  • The speed is assumed sustained for the whole transfer, which is rarely true.
  • Protocol overhead and per-file costs are not modelled.
  • The size and the speed are both converted to bytes before dividing.

Frequently asked questions

How long does it take to transfer 5 GB?

At 100 Mbps, about 6 minutes 40 seconds. At 100 MB/s, about 50 seconds. The difference is the factor of eight between bits and bytes, which is why the unit matters more than the number.

Is 100 Mbps the same as 100 MB/s?

No. 100 Mbps is 12.5 MB/s. Megabits per second and megabytes per second differ by a factor of eight, and mixing them up is the most common error in transfer estimates.

Why is my real transfer slower than this?

Because a sustained speed is an ideal. Overhead, the receiving device, many small files rather than one large one, and a drive whose cache has filled all reduce the real rate.

Related calculators