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Bandwidth Transfer Time Calculator

Estimate how long a download, upload, backup or file copy will take at a given link speed, including protocol overhead.

Transfer Details
Estimated Transfer Time
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Same Transfer at Common Speeds
LinkSpeedTime

About the Bandwidth Calculator

The classic trap in transfer-time estimates is mixing up bits and bytes. Network links are rated in bits per second (a 100 Mbps connection moves 100 million bits each second), while file sizes are shown in bytes. Divide by eight, subtract real-world protocol overhead, and that “100 Mbps” link realistically moves around 11 megabytes per second. This calculator does the conversion for you and lets you dial in an overhead percentage — 5–10% is typical for TCP/IP on a clean link, more over VPNs or Wi-Fi.

It is useful for planning backup windows, estimating cloud migration time, setting expectations for offsite replication, or simply answering “how long will this 50 GB download take?” The comparison table shows the same job across common Australian NBN tiers and LAN speeds so you can see what an upgrade would actually buy.

How to Use This Tool

1
Enter the data size — the tool accepts KB through TB, so a 750 GB backup is as easy as a 4 MB photo.
2
Enter the link speed and its unit (Mbps or Gbps). Remember file sizes are in bytes; link speeds are in bits.
3
Set the protocol overhead — the default 10% is realistic for TCP transfers; use more for VPN-encrypted paths.
4
Read the estimated transfer time, and use the quick-reference table to compare common size/speed combinations at a glance.

Common Use Cases

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    Backup window planning. Will the 2 TB weekly backup finish between 10 pm and 6 am on a 100 Mbps uplink? Know before Friday, not after.
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    Cloud migration estimates. Give a client a defensible answer for how long the initial OneDrive/SharePoint sync or server-to-cloud seed will take on their actual uplink.
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    Link sizing decisions. Show the difference between 50 Mbps and 500 Mbps in minutes-per-transfer, turning an abstract plan upgrade into a business case.
  • 🚚
    Data transport sanity checks. Sometimes the answer is "post a drive": if the calculator says 9 days, AWS Snowball or a courier beats the wire.
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    Managing expectations. "The file server copy will take about 40 minutes" is a better ticket update than "it's running" — and this gives you the number.

Planning Tips

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    Backup windows. Check the nightly change set fits the window at your real upload speed, not the advertised one.
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    Cloud migrations. For multi-terabyte seeds, compare the transfer time against a physical seed/courier option.
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    Asymmetric links. Home and small-business plans upload far slower than they download — use the upload figure for offsite backup estimates.
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    Rule of thumb. Mbps ÷ 8 ≈ MB/s, then take off ~10% for overhead.

Frequently Asked Questions

Why does my 100 Mbps connection download at only about 12 MB/s?
Because bits and bytes differ by 8: 100 megabits ÷ 8 = 12.5 megabytes per second, minus protocol overhead. Marketing speaks in bits, file managers in bytes. The calculator handles the conversion so the estimate matches what users actually see.
Why was my real transfer slower than the estimate?
The calculation assumes the link is the bottleneck. In practice, disk speed on either end, VPN encryption, many small files instead of one large one, latency on high-RTT paths, and competing traffic all slow things further. Treat the result as a best case; add margin for small-file workloads.
Why is my real speed lower than this estimate?
The calculator assumes the link is dedicated to your transfer. Shared office traffic, Wi-Fi retransmissions, disk speed at either end, VPN encryption and per-file overhead on many small files all reduce real throughput.
What is the difference between GB and GiB?
GB is decimal (10⁹ bytes) and GiB is binary (2³⁰ bytes). Windows Explorer reports binary sizes, so a “100 GB” disk file shown by Windows is really about 107 GB decimal. Both units are available in the size selector.
What overhead percentage should I use?
Around 5–10% for wired TCP transfers, 10–20% over IPsec or WireGuard VPNs, and up to 30–40% on congested Wi-Fi or when copying many small files over SMB.