Enter any two values to calculate transfer time, required speed, or data moved. Choose exact decimal or binary units and adjust efficiency only when you need a planning estimate.
GB is decimal; GiB is binary.
Mbps is bits/s; MB/s is Bytes/s.
Change solve mode to enter a target time.
%
Use 100% for exact unit math. For planning, enter a measured effective-rate percentage; no one percentage applies to every network.
Try an exact scenario
The complete size, speed and time formula
All three calculations come from one relationship: data = effective rate x time. Use matching units, and remember that file sizes are normally in Bytes while network rates such as Mbps are in bits per second.
Find time
time = data in bits / (line rate x efficiency)
Find speed
line rate = data in bits / (time x efficiency)
Find data
data in Bytes = line rate x efficiency x time / 8
For decimal MB and Mbps, the familiar shortcut is seconds = MB x 8 / Mbps. For example, 100 GB at an effective 100 Mbps is 100,000 MB x 8 / 100 = 8,000 seconds, or exactly 2 hours 13 minutes 20 seconds.
Worked data-transfer examples
Worked examples for transfer time, required speed and data transferred
Question
100% effective rate
At 90% efficiency
Time for 100 GB at 100 Mbps
2h 13m 20s
2h 28m 9s
Speed for 10 GB in 10 minutes
133.333 Mbps
148.148 Mbps line rate
Data at 100 Mbps for 1 hour
45 GB
40.5 GB
Time for 1 GiB at 100 Mbps
1m 25.899s
1m 35.444s
The 90% column is an example planning assumption, not a promised result. Use your sustained measured rate whenever it is available.
GB vs GiB: choose the unit on the source
1 GB = 1,000,000,000 Bytes, while 1 GiB = 1,073,741,824 Bytes. GiB is about 7.374% larger, so selecting the wrong unit changes the answer by the same proportion. The same distinction applies to KB/KiB, MB/MiB and TB/TiB.
Estimate real transfer time without inventing one overhead rate
The exact calculation is based on sustained effective throughput. A plan speed or link rate can differ from that throughput because the source server, other traffic, protocol behavior, retransmissions, the wireless link, and storage read/write speed can each become the bottleneck.
If you measured the transfer
Enter the sustained rate and leave efficiency at 100%. The rate already reflects the path that produced it.
If you only know the line rate
Use 100% for the theoretical result, or supply your own measured or planning efficiency. Avoid treating any generic percentage as universal.
Latency is not normally added once as a fixed delay to a bulk-transfer result. It can influence the throughput a transport protocol achieves, especially when the transfer is short or the path constrains the amount of unacknowledged data. In this calculator, reflect that effect in the sustained speed or efficiency.
Definitions and methodology
The unit factors are exact. Decimal prefixes follow the International System of Units, and binary prefixes follow the IEC names documented by NIST. The calculator performs all conversions in Bytes, bits per second and seconds before displaying the selected unit.
Exact answers about download and data-transfer calculations
How do I calculate download time?
Convert the file size to bits and the transfer speed to bits per second, then divide size by speed. For decimal MB and Mbps: time in seconds = MB x 8 / Mbps. At less than 100% efficiency, divide by the efficiency as a decimal as well.
How do I calculate the required download speed?
Divide the data size in bits by the target time in seconds. If you expect less than 100% efficiency, divide by the efficiency decimal too. Moving 10 GB in 10 minutes requires 133.333 Mbps at 100% efficiency or about 148.148 Mbps at 90%.
How do I calculate how much data can be transferred?
Multiply the transfer speed in bits per second by the duration in seconds and the efficiency decimal, then divide by 8 to convert bits to Bytes. At 100 Mbps for one hour and 100% efficiency, the theoretical amount is 45 GB.
How long does 100 GB take to download at 100 Mbps?
Exactly 8,000 seconds, or 2 hours 13 minutes 20 seconds, at a constant 100 Mbps effective rate using decimal GB. If 100 Mbps is the line rate and efficiency is 90%, the adjusted estimate is about 2 hours 28 minutes 9 seconds.
Why do I multiply a file size by 8?
File sizes are normally expressed in Bytes, while network rates such as Mbps use bits. One Byte contains 8 bits, so multiplying the byte amount by 8 makes the units compatible before dividing by a bit-per-second rate.
What is the difference between GB and GiB in download calculations?
GB is decimal: 1 GB = 1,000,000,000 Bytes. GiB is binary: 1 GiB = 1,073,741,824 Bytes. A 100 GiB transfer contains about 7.374% more data than a 100 GB transfer, so it takes proportionally longer at the same effective rate.
What does transfer efficiency mean in this calculator?
Efficiency is the percentage of the entered line rate that carries the data being counted. Use 100% for pure unit math, or enter a measured or planning percentage. The calculator does not assume one universal Ethernet or Wi-Fi loss rate.
Can I use this calculator for uploads and local file transfers?
Yes. The size-rate-time relationship is the same for downloads, uploads, backups and local transfers. Enter the effective upload or transfer rate, choose the correct units, and use an efficiency value appropriate to that path.
Does network latency belong in the download-time formula?
Not as a single number added to the result. For a sustained bulk transfer, size divided by achieved throughput determines most of the duration. Latency can reduce achieved throughput through protocol behavior, but it should be reflected in the measured rate or efficiency rather than added once as a fixed delay.
