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Data Transfer Calculator

Enter file size and transfer speed to calculate transfer time across USB, Ethernet, Wi-Fi, and storage interfaces. Or flip it: size plus deadline gets the required speed, speed plus time gets the data that fits.

Calculate:

Configuration

Mbps
Latency & TCP window
Estimated Transfer Time
6m 40s
about 250,000 pages of PDFs

Showing the most common interface per family. Switch to All interfaces or a category to see the full list.

Speed Comparison

Estimated time for the current file size, sorted fastest to slowest.

01
NVMe Gen5 SSD
112 Gbps
3s
02
NVMe Gen4 SSD
56 Gbps
7s
03
WiFi 7 (be)
46 Gbps
8s
04
Thunderbolt 4
40 Gbps
10s
05
USB4 40 Gbps
40 Gbps
10s
06
USB 3.2 Gen 2x2
20 Gbps
20s
07
10 Gigabit Ethernet
10 Gbps
40s
08
WiFi 6
9.6 Gbps
41s
09
USB 3.0
5 Gbps
1m 20s
10
Gigabit Ethernet
1 Gbps
6m 40s
Selected
11
USB 2.0
480 Mbps
13m 53s

How to use this tool

  1. Choose what to solve for

    The Calculate selector has four modes. Transfer time turns a file size and a connection speed into an expected duration. Required speed turns a file size and a deadline into the minimum Mbps you need. Data amount turns a link speed and a time window into how much you can move. Connection finder turns a single Mbps target into the smallest interface that meets it, plus the next one up if you want headroom.

  2. Enter the size

    For Transfer time and Required speed, type the file or folder size and pick the unit (MB, GB, or TB). For Data amount and Connection finder, skip size.

  3. Enter the speed or target

    For Transfer time and Data amount, pick a preset interface (USB 2.0 through USB4 v2 80 Gbps, Thunderbolt 3/4/5, 1 through 100 Gigabit Ethernet, WiFi 5/6/6E/7/8, SATA HDDs, SATA SSD, NVMe Gen3/4/5) or enter a custom Mbps figure. For Connection finder, enter just the Mbps you want.

  4. Enter the time

    For Required speed and Data amount, type the time window in hours, minutes, and seconds (for example 0h 13m 20s for 100 GB over 10 GbE). The tool converts this to seconds internally so the URL stays compact.

  5. Read the result

    The hero answer shows the requested value. The interface table below switches to fit the mode: sorted by time in Transfer time, tagged meets it / best fit in Required speed, showing data moved per interface in Data amount, and flagged minimum / recommended in Connection finder.

  6. Compare two connections

    Available in Transfer time mode. Toggle Compare to put two interfaces side-by-side and see how many minutes a faster link saves on the same file size.

  7. Model WAN latency (optional)

    Available in Transfer time mode. Open the latency panel and enter a round-trip time plus a TCP receive window. The tool recomputes the transfer time against the bandwidth-delay product ceiling (window divided by RTT), which shows the real throughput a long-distance link delivers instead of the naive size-over-speed figure.

About this tool

The Data Transfer Calculator solves the copy equation in four directions. Give it file size and speed and it returns transfer time across USB, Ethernet, Wi-Fi and storage interfaces. Give it file size and a deadline and it returns the required Mbps, with every preset interface tagged whether it meets the bar. Give it speed and a time window and it returns the data that fits, anchored to something tangible like how many pages of PDFs it is. And if all you know is how fast you want it, Connection finder finds the smallest interface that meets the target plus the next one up if you want headroom.

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

With RTT enabled, the model computes window bytes x 8 divided by RTT and takes the smaller of that ceiling and link speed. Scaling expands the allowed window range but never replaces the entered buffer. At 100 ms RTT, a 256 KiB scaled receive window limits a 1 Gbps link to about 20.97 Mbps. Leave RTT empty to use the simple size-over-speed calculation.

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.

1 TB over USB 3.0
The baseline external SSD transfer
View details ➜
1 TB over Thunderbolt 4
40 Gbps enclosure territory
View details ➜
1 TB over Gigabit Ethernet
The NAS over wire baseline
View details ➜

Data transfer comparisons

Head-to-head breakdowns of the interface and network speed questions behind every big copy: USB generations, Thunderbolt versus USB4, and WiFi 6 versus WiFi 7 when it is time to move the file.

USB 3.0 (5 Gbps) vs USB 3.2 Gen 2 (10 Gbps)
Same USB-C port, double the pipe - if your drive can keep up.
Read comparison ➜
Thunderbolt 4 vs USB4
Same connector, same top speed, different promises.
Read comparison ➜
WiFi 6 (9.6 Gbps peak) vs WiFi 7 (46 Gbps peak)
Peak link math with real-world limits called out separately.
Read comparison ➜

Frequently asked questions

How long does it take to transfer 1 TB over Gigabit Ethernet?
At a theoretical 1000 Mbps (125 MB/s), 1 TB takes about 2 hours and 13 minutes in ideal conditions. Real-world speeds over Gigabit Ethernet typically top out around 110-115 MB/s due to TCP overhead, so budget closer to 2.5 hours for a full 1 TB copy.
Why is my real transfer speed slower than the cable's rated speed?
Rated speeds are raw signaling rates in bits per second. Protocol overhead (TCP/IP, USB framing, filesystem operations), encryption, small file latency, and the slowest device in the chain (often the disk, not the cable) all reduce usable throughput. A USB 3.0 port rated 5 Gbps usually delivers around 400 MB/s in practice, not the theoretical 625 MB/s. Transfers also draw power; the electricity cost calculator shows what a long copy job adds to a PC's running cost.
What's the difference between megabits (Mbps) and megabytes (MB/s)?
There are 8 bits in a byte, so 1000 Mbps equals 125 MB/s. Network speeds and ISP plans are advertised in megabits per second, while file sizes and storage speeds are measured in megabytes per second. Dividing Mbps by 8 gives you the MB/s figure you actually see when copying files.
How fast is WiFi 6 compared to Gigabit Ethernet for file transfers?
WiFi 6 can exceed Gigabit Ethernet on paper (up to ~9.6 Gbps theoretical) but real-world throughput usually lands between 500 Mbps and 1.5 Gbps depending on distance, interference, and client hardware. For a single large file transfer, wired Gigabit is still more consistent. WiFi 6E or WiFi 7 can edge ahead in ideal conditions.
Is USB 4 or Thunderbolt 4 faster for copying files?
Thunderbolt 4 guarantees 40 Gbps and PCIe 32 Gbps tunneling. USB4 products can be rated at 20 Gbps or 40 Gbps, with feature support varying by implementation. A fully featured 40 Gbps USB4 setup can deliver comparable real-world speeds, but check the port, cable, and enclosure instead of assuming parity.
Does file structure affect transfer speed?
Yes, significantly. Transferring one 50 GB file hits near maximum throughput, but copying 50 GB of small files (thousands of photos, say) can be 5-10x slower because every file has filesystem and metadata overhead. For large migrations, compressing into an archive first is often faster end to end.
Can the calculator work out required speed or total data size?
Yes. Flip Calculate to Required speed and enter the file size plus your deadline (for example, 100 GB before a 15-minute cutover) - the tool returns the required Mbps and marks every preset interface that meets it. Flip to Data amount and enter your link speed plus the time window (for example, one hour on Gigabit Ethernet) to see how much data fits. All solves live in one tool and save to the URL.
Can I find a suitable connection just from a speed target?
Yes. Choose Connection finder, enter the Mbps you need (for example 500 Mbps), and the tool shows the smallest preset that meets the target plus the next one up as a headroom option. Useful when you know the download rate you want but not which cable, port, or WiFi generation actually delivers it.
How does network latency affect file transfer time?
On a long-distance link, latency can cap throughput far below the link rate. TCP only sends one receive window of data before waiting for an acknowledgment, so on a high-RTT path the effective speed becomes window size divided by round-trip time. 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. Use the latency panel to model this.
Why is my WAN or cloud transfer so much slower than my connection speed?
The bottleneck is usually the bandwidth-delay product, not the link. The bandwidth-delay product is link speed times round-trip time, and it is the amount of data that must be in flight to fill the pipe. When your TCP receive window is smaller than it, throughput collapses to window divided by RTT. Enable RFC 1323 window scaling on both endpoints, use SMB Multichannel or another explicitly multistream tool, or run multiple partitioned rsync jobs when parallelism is appropriate. Also check that no middlebox is stripping the TCP window scaling option.
What is TCP window scaling and should I enable it?
RFC 7323 window scaling expands the receive-window range beyond 65,535 bytes to just below 1 GiB. It does not automatically allocate that maximum. Enter the actual effective receive window in KiB. The model uses the entered value, clamped to the protocol limit for the selected mode.

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