Data Transfer Calculator
Calculate how long it takes to move data across networks and drives.
Configuration
Latency & TCP window model
Enable to model WAN and cloud-migration throughput with the TCP receive window and bandwidth-delay product.
Speed Comparison
How to use this tool
Enter the file size
Type the size of the file or folder you want to copy and pick the unit (MB, GB, or TB). The calculator converts the input into bits behind the scenes using the same decimal/SI convention drive manufacturers use (1 GB = 1 billion bytes).
Pick the interface
Choose the link the transfer will run over (USB 2.0/3.0/3.2/4, Thunderbolt 3/4, Gigabit or 10-Gigabit Ethernet, Wi-Fi 5/6/7, SATA SSD, or NVMe Gen4) or enter a custom Mbps figure for any undocumented interface.
Read the transfer time
The tool returns the expected copy time broken down into days, hours, minutes, and seconds. Treat the result as a theoretical floor - real-world overhead is lower but the figure is useful for comparison and planning.
Compare two connections
Toggle Compare to put two interfaces side-by-side and see exactly how many minutes (or hours) you'd save by upgrading from Wi-Fi to Ethernet, USB 3.0 to USB 4, or any other pair.
Model WAN latency (optional)
For cross-site or cloud transfers, open the latency panel and enter a round-trip time (or pick a preset like transatlantic or satellite) plus a TCP receive window. The tool recomputes the transfer time against the bandwidth-delay product ceiling, window divided by RTT, so you see the throughput a long-distance link actually delivers rather than the naive size-over-speed figure.
About this tool
The Data Transfer Calculator estimates how long it will take to copy a file of any size across any interface, including USB 2.0 through USB 4, Thunderbolt, Gigabit and 10-Gigabit Ethernet, WiFi 5/6/7, SATA SSDs, or NVMe Gen4 drives. Pick a preset or punch in your own Mbps figure, enter the file size in MB, GB, or TB, and the tool returns a realistic transfer time broken down into days, hours, minutes, and seconds.
For WAN and cloud migrations it also models the TCP receive window and bandwidth-delay product, the effect that caps long-distance throughput far below the link rate. Open the latency panel, enter a round-trip time (or pick a preset like transatlantic or satellite), and the tool shows the effective Mbps, the link utilization, and whether the window or the link is the bottleneck. A 1 Gbps link at 100 ms RTT with the default 64 KB window delivers about 5.24 Mbps, which is 0.52% of the rated speed.
It's the quickest way to reality check a backup plan, decide whether that external SSD is worth the money, or work out if you can finish a 200 GB game download before bed. Switch on Compare mode to put two connections head to head and see exactly how many minutes (or hours) you'd save by upgrading from WiFi to Ethernet, or from USB 3.0 to USB 4.
Formula
Transfer time is file size in bits divided by link speed in bits per second. The calculator converts your input to bits (1 byte = 8 bits, 1 GB = 8,000,000,000 bits using the decimal/SI convention drives are sold under), then divides by the Mbps figure times 1,000,000. Real-world overhead, such as TCP, USB framing, and filesystem operations, isn't modeled, so treat the result as an optimistic floor.
Latency and the bandwidth-delay product
When the optional round-trip time is set, the tool computes the TCP throughput ceiling as receive window divided by RTT and uses the smaller of that and the link speed. That ceiling is the bandwidth-delay product at work: on a high-latency link the window can't stay full long enough, so the link delivers a fraction of its rated speed. With RFC 1323 window scaling enabled the window can grow up to 1 GiB and the link fills again. Leave the RTT empty and the tool behaves exactly as the size-over-speed calculator.
When to use it
Use it before buying storage or networking gear to see whether the spec jump is worth the price, when planning a big one-off copy like a photo library migration, or when deciding between wired and wireless for a specific workload. For cloud and WAN migrations, use the latency panel to avoid committing to a cutover date the TCP window won't let you meet. Pair it with the RAID Calculator when sizing a NAS and the Display Bandwidth Calculator if you're comparing video cable throughput against the same numbers.
Popular transfer scenarios
Pre-computed copy times for the file size + interface combinations visitors ask about most.
Frequently asked questions
How long does it take to transfer 1 TB over Gigabit Ethernet?
Why is my real transfer speed slower than the cable's rated speed?
What's the difference between megabits (Mbps) and megabytes (MB/s)?
How fast is WiFi 6 compared to Gigabit Ethernet for file transfers?
Is USB 4 or Thunderbolt 4 faster for copying files?
Does file structure affect transfer speed?
How does network latency affect file transfer time?
Why is my WAN or cloud transfer so much slower than my connection speed?
What is TCP window scaling and should I enable it?
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