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Bandwidth and download time calculator

Download or upload time for a file at a given speed, the data a link moves in a set time, and a website's monthly bandwidth from page views.

Drafted with AI writing toolsUpdated Checked examples: 6

Internet plans quote megabits per second (Mbit/s); download dialogs often show megabytes per second (MB/s), 8 times smaller.
%
Share of the line rate lost to packet headers. TCP/IPv4 over Ethernet carries 1460 payload bytes per 1538 bytes on the wire, about 5%.
Try
Transfer time
1 h 10 min 10 s
Transfer time: 1 h 10 min 10 s
Transfer time in seconds
4,210.53s
Data
50GB / 46.566GiB
Payload speed after overhead
95Mbit/s

Moving 50 GB at 100 Mbit/s with 5% overhead takes 1 h 10 min 10 s; speeds are in bits and sizes in bytes, so the size is multiplied by 8 first.

Same transfer at other speeds

10 Mbit/s11 h 41 min100 Mbit/s1 h 10 min1 Gbit/s7 min 1 s10 Gbit/s42.1 sYour 100 Mbit/s1 h 10 min
How it's calculated S

  1. Size in bits

    5×1010 B×8=4×1011 bit5 \times 10^{10}\ \text{B} \times 8 = 4 \times 10^{11}\ \text{bit}

  2. Payload speed

    100 Mbit/s×(1−5%)=95 Mbit/s100\ \text{Mbit/s} \times (1 - 5\%) = 95\ \text{Mbit/s}

    Headers, acknowledgements and retransmissions share the line with your data.

  3. Divide size by speed

    t=4×10119.5×107=4,210.53 st = \frac{4 \times 10^{11}}{9.5 \times 10^{7}} = 4{,}210.53\ \text{s}

About the bandwidth and download time calculator

Transfer time is the size in bits divided by the speed in bits per second: t = 8 × bytes ÷ (rate × (1 − overhead)). Here S_B is file size in bytes, r is speed in bits per second, h is the overhead fraction, B_m is monthly bytes, N is monthly page views and P_B is bytes per page. The factor of 8 is there because internet plans quote megabits per second while files are measured in bytes. The other two modes run the same equation the other way, for the data a link moves in a set time, or multiply page views by page weight for a website's monthly traffic.

The default, a 50 GB download on a 100 Mbit/s plan with 5% protocol overhead, takes 1 h 10 min 10 s; with no overhead it would take 1 h 6 min 40 s. A site with 100,000 monthly views of a 2 MB page serves 200 GB a month.

Real downloads can be slower than the result when the server, Wi-Fi or a congested route caps the speed below the plan's rate. Sizes follow IEC 80000-13: 1 GB is 10^9 bytes and 1 GiB is 2^30 bytes.

How to calculate download time

Multiply the file size in bytes by 8 to get bits, then divide by the connection speed in bits per second: t = 8 × size ÷ speed. A 50 GB download is 400,000 megabits, so a 100 Mbit/s line needs 4,000 seconds, or 1 h 6 min 40 s; with 5% protocol overhead, about 1 h 10 min 10 s.

Bits, bytes and binary units

  • Bits versus bytes. Internet plans quote megabits per second, while download dialogs show megabytes per second. Divide by 8: 100 Mbit/s is 12.5 MB/s, and 1 Gbit/s is 125 MB/s.
  • Decimal versus binary sizes. 1 GB is 10⁹ bytes and 1 GiB is 2³⁰ = 1,073,741,824 bytes. At 1 Gbit/s, 1 GB takes 8 seconds and 1 GiB takes 8.59 seconds.
  • Network rates are decimal. 100 Mbit/s means 100,000,000 bits per second. NIST's binary-prefix page defines both families of units.

How long does 1 GB take to download?

At the full line rate, with no overhead:

  • 10 Mbit/s: 800 s, or 13 min 20 s
  • 100 Mbit/s: 80 s
  • 1 Gbit/s: 8 s
  • 10 Gbit/s: 0.8 s

Multiply by the size in GB for larger files: 50 GB at 100 Mbit/s takes 50 × 80 = 4,000 s.

Protocol overhead

Part of every frame on the wire is headers, not your data. RFC 6349, section 4.1.1 works through Ethernet with a 1500-byte MTU: each full frame carries 1460 bytes of TCP payload in 1538 bytes of wire time, about 94.9%.

That is where the 5% allowance comes from. Apply it to a line rate only: a speed test or a download dialog already reports payload throughput, so subtracting 5% again counts the same loss twice.

Data moved in a set time

Run the formula backward: data = speed × time ÷ 8. At 100 Mbit/s, one hour moves 100 × 3,600 ÷ 8 = 45,000 MB, or 45 GB. With 5% overhead it moves 42.75 GB.

Website bandwidth per month

Multiply monthly page views by the average page weight, which a browser's network panel reports. 100,000 views of a 2 MB page is 200 GB a month, about 6.67 GB a day. Spread evenly over 30 days, that averages 0.617 Mbit/s.

Traffic arrives in peaks, so size hosting for the busiest hour, which can be several times the average. Caching and a CDN cut what the origin server has to send.

Transfer and traffic examples

ScenarioData GBTransfer secondsAverage Mbit/s
Default504210.526316—
No overhead504000—
One hour amount42.75——
Monthly default200—0.617284
Binary page weight209.7152—0.626389

The first three rows use 100 Mbit/s, and only No overhead drops the 5% allowance. Monthly default is 100,000 views of 2 MB over 30 days.

Binary page weight changes the page to 2 MiB and the month to 31 days. A dash marks a figure that belongs to another kind of estimate.

Common download-time mistakes

  • Reading Mbit/s as MB/s. The estimate comes out 8 times too short.
  • Using the download speed for an upload. Many plans upload far slower than they download, so use the upload rate for backups and video calls.
  • Expecting Windows to match the label. A 50 GB file shows as 46.57 there, because Windows counts GiB but labels them GB.
  • Ignoring the slowest link. A server's own limit, a weak Wi-Fi signal or a slow disk can cap a transfer below the plan's rate.

Supported units and durations

  • Sizes in MB, GB, TB, MiB, GiB or TiB, and speeds in kbit/s, Mbit/s, Gbit/s, MB/s or MiB/s.
  • Durations accept forms such as 1 h or 1 min 30 s.
  • Overhead runs from 0% to 90% of the line rate.

For unit conversions alone, use the data storage converter. For storage planning, use the RAID capacity calculator.

Worked examples

50 GB at 100 Mbit/s with no overhead

I want to find
Transfer time
Data size
50 GB
Connection speed
100 Mbit/s
Protocol overhead
0%
Transfer time in seconds
4,000 s
Transfer time
1 h 6 min 40 s

Checked against: 50e9 × 8 / 100e6 = 4000 s

Same transfer with 5% overhead

I want to find
Transfer time
Data size
50 GB
Connection speed
100 Mbit/s
Protocol overhead
5%
Transfer time in seconds
4,210.53 s
Payload speed after overhead
95 Mbit/s

Checked against: 4000 / 0.95 = 4210.526315…

1 GiB at 1 Gbit/s (binary size, edge)

I want to find
Transfer time
Data size
1 GiB
Connection speed
1 Gbit/s
Protocol overhead
0%
Transfer time in seconds
8.59 s

Checked against: Independent calculation

One hour at 100 Mbit/s

I want to find
Data moved in a time
Connection speed
100 Mbit/s
Time spent transferring
1 h
Protocol overhead
0%
Data
45 GB
Data
41.91 GiB

Checked against: 100e6 × 3600 / 8 = 45e9 B

Questions

How long does it take to download 1 GB at 100 Mbps?

About 80 seconds at the full line rate: 1 GB is 8,000 megabits, and 8,000 ÷ 100 = 80 s. With 5% protocol overhead it takes about 84 s. At 10 Mbit/s the same file takes 13 min 20 s, and at 1 Gbit/s about 8 s, as long as the server and Wi-Fi keep up.

What is the difference between Mbps and MB/s?

Mbps (megabits per second) measures network speed, while MB/s (megabytes per second) is how browsers and download managers show progress. One byte is 8 bits, so divide Mbps by 8: a 100 Mbit/s plan tops out at 12.5 MB/s, and 1 Gbit/s at 125 MB/s. Protocol overhead lowers the figure you see by a further few percent.

Why is my download slower than my internet speed?

Part of the gap is protocol overhead: over Ethernet, TCP/IPv4 carries 1,460 bytes of data in each full 1,538-byte frame on the wire, so about 5% of the line rate goes to headers, preamble and inter-frame gap. The rest comes from the server's own limit, Wi-Fi signal, congestion on the route, or other devices sharing the connection.

How much bandwidth does a website need per month?

Multiply monthly page views by the average page weight, which your browser's network panel shows. 100,000 views of a 2 MB page is 200 GB a month, about 6.7 GB a day or an average of 0.62 Mbit/s. Visits bunch up in busy hours, so size hosting and caching for several times that average.

Is 1 GB 1,000 MB or 1,024 MB?

Under the SI and IEC 80000-13 prefixes, 1 GB is 1,000 MB, or 10^9 bytes, while 1 GiB (gibibyte) is 1,024 MiB, or 2^30 = 1,073,741,824 bytes. Network speeds and drive labels use decimal units. Windows counts in binary units but labels them GB, so a 50 GB file shows there as 46.57.

About this calculator

t=8×SBr×(1−h)Bm=N×PB\begin{aligned} t &= \frac{8 \times S_B}{r \times (1 - h)} \\[4pt] B_m &= N \times P_B\end{aligned}

Sources

  1. IEC 80000-13:2008 — decimal (kB, MB, GB) and binary (KiB, MiB, GiB) prefixes for bytes
  2. IEEE 802.3 Ethernet: 8-byte preamble, 14-byte header, 1500-byte payload, 4-byte FCS and 12-byte inter-frame gap (1538 bytes per full frame)
  3. NIST — Prefixes for binary multiples

Checked against references

This calculator includes 6 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.

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