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Download Time, File Size and Transfer Rate

Estimate download duration, required sustained transfer speed or transferable file size with decimal and binary data units and editable results.

  • Formula & worked example
  • Private in your browser
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 750 MB file takes 60 seconds at a sustained 100 Mbit/s: 750 million bytes × 8 bits per byte ÷ 100 million bits per second.

File size = sustained data rate × time; time = file size ÷ rate; rate = file size ÷ time.

Worked example

Enter these known values and leave the other values blank.

File size
750 MB
Sustained transfer speed
100 Mbit /s
Transfer duration
0:1:0 hrs / min / sec

Assumptions and limitations

  • Enter any two known quantities and leave the third blank. The rate is a constant sustained payload rate, in the chosen data unit per second.
  • Decimal kB/MB/GB use powers of 1000. Binary KiB/MiB/GiB use powers of 1024. One byte is exactly eight bits; MB/s and Mbit/s differ by a factor of eight.
  • This ideal payload estimate excludes protocol overhead, connection setup, contention, retransmissions, compression and changing network speeds. Use measured sustained throughput for a more realistic estimate.
  • All quantities are nonnegative. An empty file at positive speed takes zero time; zero speed over a known positive interval transfers zero data. A positive file cannot transfer in zero time or at zero speed.
  • Zero file size with zero speed leaves time undetermined. Zero file size with zero duration leaves rate undetermined. No finite result is supplied for division by zero.
  • Mixed duration controls retain their component order. Months are fixed at 2629800 seconds and years at 31557600 seconds, using a 365.25-day Julian year; they are not actual calendar intervals.
  • Locked conflicting known quantities are reported. This is a data throughput calculation, not radio frequency bandwidth or a guarantee of your connection performance.

Common questions

How long does a 1 GB download take at 100 Mbps?

Using decimal units and a sustained 100 million bits per second, 1 GB contains 8 billion bits and takes 80 seconds before overhead.

Why is MB per second different from Mbps?

MB/s counts bytes and Mbps counts bits. Eight bits make one byte, so 100 Mbit/s equals 12.5 MB/s.

Can I solve for the speed needed to meet a deadline?

Yes. Enter file size and a positive transfer duration, then leave speed blank. The result is the required sustained payload rate.

What happens at zero speed?

A positive file has no finite completion time at zero throughput. An empty file paired with zero throughput does not determine a unique duration.

References

Preserve all three transfer relationships and guard division by exactly zero. Empty-file zero/zero inputs leave duration or rate undetermined instead of returning Infinity or NaN. A positive file requires positive throughput and a positive transfer duration. Preserve nonnegative source domains and valid zero-file or zero-throughput forward cases.

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