How many MB/s is 100 Mbit/s?

12.5 MB/s at most. There are eight bits in a byte, so you divide the bit rate by eight: 100 Mbit/s gives 12.5 MB/s, 1 Gbit/s gives 125 MB/s and 10 Gbit/s gives 1250 MB/s. Protocol overhead then takes a few per cent off, so expect around 11.9 MB/s of payload on a healthy 100 Mbit/s link.

How long does it take to transfer 1 TB over a 1 Gbit/s link?

About 2 hours 13 minutes at the theoretical maximum: 1 TB is 8 trillion bits, which at 1 Gbit/s takes 8000 seconds. Allow 5% for protocol overhead and it becomes roughly 2 hours 20 minutes. A 1 TiB transfer is about 10% larger, so closer to 2 hours 34 minutes.

What is the difference between GB and GiB?

A gigabyte is 10^9 bytes and a gibibyte is 2^30 bytes, about 7.4% more. The binary prefixes KiB, MiB and GiB are standardised in IEC 80000-13 precisely to end that ambiguity. Storage and network vendors quote decimal units while many operating systems report binary ones, which is why a 1 TB disk shows as 931 GiB.

How much protocol overhead should I allow?

Around 5% is fair for bulk TCP transfer over a clean path: headers, acknowledgements and framing take a few per cent, and a well-tuned stream reaches most of the wire rate. Allow 10% or more for small files, high latency, packet loss, or encrypted tunnels that add their own headers. On long paths, latency and window size matter as much as overhead.

Bandwidth & Transfer Time Calculator

Bandwidth and transfer time calculator: how long a given amount of data takes over a given link, with a protocol overhead allowance, throughput in MB/s and data per day.

Amount of dataUnitLink speedUnitProtocol overhead (%)

Note the units: network speeds are quoted in bits per second, file sizes in bytes. A 100 Mbit/s link moves at most 12.5 MB/s. The overhead allowance covers TCP/IP headers and acknowledgements (~5% is typical for bulk transfer).

Realistic transfer time

14.0 min

theoretical minimum 13.3 min at 12.50 MB/s

If the link ran flat out

Throughput: 12.50 MB/s
Data per day: 1080.0 GB
Data per 30-day month: 32.40 TB

About Bandwidth & Transfer Time Calculator

The Bandwidth and Transfer Time Calculator answers a question that comes up on every migration and every backup design: how long will this much data take over this link? Enter the amount of data and the link speed, adjust the protocol overhead allowance, and you get a realistic transfer time alongside the theoretical minimum, the throughput in MB/s, and how much the link would carry in a day and in a 30-day month if it ran flat out. Sizes accept decimal and binary units, rates accept bits or bytes.

Two unit conventions collide here and the result is a factor-of-eight error. Link rates are quoted in bits per second, file sizes in bytes, so a 100 Mbit/s link moves at most 12.5 MB/s and a gigabit link about 125 MB/s. On top of that, storage vendors use decimal prefixes while operating systems often report binary ones, standardised as KiB, MiB and GiB in IEC 80000-13: a 1 TB disk holds only 0.909 TiB. Mixing the two is how a transfer window planned for six hours becomes a weekend.

The overhead field is the honest part of the calculation. A wire rate is never fully available to payload: TCP and IP headers, acknowledgements, framing and retransmissions all take a share, and roughly 5% is a reasonable allowance for a bulk transfer over a well-behaved path. The tool shows the ideal figure and the adjusted one together so you can see how much of the gap is protocol rather than luck. Latency and window size are not modelled, so a long fat path with a small receive window will still fall short. Everything runs in the browser.

How to use it

1Enter the amount of data to move and pick its unit: decimal KB, MB, GB or TB, or binary MiB, GiB or TiB.
2Enter the link speed and pick its unit: Mbit/s, Gbit/s, kbit/s or MB/s.
3Set a protocol overhead allowance; 5% is a reasonable default for a bulk transfer.
4Read the realistic transfer time, with the theoretical minimum and the throughput in MB/s beneath it.
5Check the flat-out figures to see how much the link carries per day and per 30-day month.
6Raise the overhead percentage to model a lossy or high-latency path and see the effect on the window.

Common use cases

-Estimating how long a multi-terabyte migration will take before booking the maintenance window.
-Sizing an uplink for nightly backups that have to finish before the working day starts.
-Checking whether a monthly transfer allowance can be exhausted by a link running continuously.
-Converting a quoted Mbit/s figure into the MB/s a colleague will actually see in a file manager.
-Planning replication between two sites and confirming the link can carry a day's change volume.

Frequently asked questions

How many MB/s is 100 Mbit/s?: 12.5 MB/s at most. There are eight bits in a byte, so you divide the bit rate by eight: 100 Mbit/s gives 12.5 MB/s, 1 Gbit/s gives 125 MB/s and 10 Gbit/s gives 1250 MB/s. Protocol overhead then takes a few per cent off, so expect around 11.9 MB/s of payload on a healthy 100 Mbit/s link.
How long does it take to transfer 1 TB over a 1 Gbit/s link?: About 2 hours 13 minutes at the theoretical maximum: 1 TB is 8 trillion bits, which at 1 Gbit/s takes 8000 seconds. Allow 5% for protocol overhead and it becomes roughly 2 hours 20 minutes. A 1 TiB transfer is about 10% larger, so closer to 2 hours 34 minutes.
What is the difference between GB and GiB?: A gigabyte is 10^9 bytes and a gibibyte is 2^30 bytes, about 7.4% more. The binary prefixes KiB, MiB and GiB are standardised in IEC 80000-13 precisely to end that ambiguity. Storage and network vendors quote decimal units while many operating systems report binary ones, which is why a 1 TB disk shows as 931 GiB.
How much protocol overhead should I allow?: Around 5% is fair for bulk TCP transfer over a clean path: headers, acknowledgements and framing take a few per cent, and a well-tuned stream reaches most of the wire rate. Allow 10% or more for small files, high latency, packet loss, or encrypted tunnels that add their own headers. On long paths, latency and window size matter as much as overhead.