Bandwidth Calculator
Calculate transfer time from a connection speed, or calculate the bandwidth required to move a file, backup, dataset, or replication stream inside a target window. The math stays local in your browser.
Inputs
Hours, minutes, seconds.
Results
Core formulas: adjusted bits = bytes x 8 x (1 + overhead),
usable bps = line bps x efficiency, and
time = adjusted bits / usable bps.
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Bandwidth, throughput, and transfer windows
Bandwidth is the nominal capacity of a link, usually advertised in bits per second. Throughput is the useful rate an application actually gets after protocol overhead, congestion, retransmits, encryption, storage speed, and software limits. This calculator separates those ideas so planning numbers do not assume a perfect wire.
Use transfer-time mode when you already know the available connection speed. Use required-bandwidth mode when a backup, file move, replication job, or migration must finish inside a fixed window. The efficiency input models how much of the nominal line rate is usable for payload data, while overhead models extra traffic that must also cross the link.
Network rates are normally decimal: 1 Mbps is 1,000,000 bits per second and 1 Gbps is 1,000 Mbps. Storage sizes may be decimal or binary depending on the tool reporting them. The unit convention selector makes that assumption explicit, which matters for large TB and PB transfers.
Formula and assumptions
Data bytes: amount x unit multiplier
Adjusted bits: data bytes x 8 x (1 + overhead/100)
Usable bandwidth: nominal bandwidth x efficiency/100
Transfer time: adjusted bits / usable bandwidth
Required nominal bandwidth: adjusted bits / target seconds / (efficiency/100)
The calculator assumes steady-state throughput. It does not model TCP slow start, Wi-Fi airtime contention, ISP congestion, storage I/O limits, or per-flow shaping.
Example transfer sizes
| Scenario | Useful inputs | Planning note |
|---|---|---|
| 100 GB file copy over 1 Gbps | 100 GB, 1 Gbps, 5% overhead, 85% efficiency | Expect roughly 16-17 minutes, not the perfect-wire 13.3 minutes. |
| 2 TB backup in 8 hours | 2 TB, required-bandwidth mode, 8 hours | Use a realistic efficiency percentage for backup software and storage limits. |
| Cloud migration over 10 Gbps | Dataset size, 10 Gbps, measured efficiency | Large migrations are often limited by storage, API, or per-flow behavior before line rate. |
| Replication across a WAN | Binary size units, higher overhead, lower efficiency | Latency, encryption, and packet loss can reduce usable throughput materially. |
FAQs
What is the difference between Mbps and MB/s?
Mbps is megabits per second. MB/s is megabytes per second. Divide Mbps by 8 to get MB/s before overhead and efficiency.
Why is my real transfer slower than the calculated perfect speed?
Real transfers pay for headers, encryption, retransmits, disk I/O, congestion, application limits, and sometimes Wi-Fi contention.
Should I use GB or GiB?
Use decimal GB when your source reports SI storage units. Use binary mode when your source is closer to GiB/TiB values.
Can this size internet service for a team?
For per-user capacity planning, use the related Network Throughput Planner because it includes user count, peak factor, and traffic split.
Is this calculator private?
Yes. Inputs are processed locally and are not submitted to a server.
Disclaimer
Bandwidth estimates are planning aids. Validate production designs with measured throughput, vendor documentation, carrier service terms, and application behavior.