Speed Calculator

Calculate real-world transfer speeds for any standard. See how long it takes to transfer files over USB, Thunderbolt, or Ethernet.

How to Use

  1. 1
    Choose a cable standard

    Select the cable standard like USB 3.2 Gen 2, Thunderbolt 4, or 10G Ethernet.

  2. 2
    Enter the file size

    Type the size of the file or data set you want to transfer.

  3. 3
    View transfer time estimates

    See theoretical maximum and realistic transfer times accounting for protocol overhead.

About

Theoretical bandwidth and real-world transfer speeds are rarely the same. Understanding why requires looking at every layer of the data transfer pipeline. At the physical layer, encoding schemes like 8b/10b (used in USB 3.0) convert every 8 bits of data into 10 bits on the wire, immediately consuming 20 percent of the raw bandwidth for clock recovery.

Above the physical layer, protocol overhead adds packet headers, checksums, acknowledgments, and flow control signals. USB 3.2 Gen 2 advertises 10 Gbps, but after encoding and protocol overhead, maximum throughput for file transfers is typically around 7-8 Gbps. Thunderbolt 4 at 40 Gbps delivers roughly 32-36 Gbps of usable bandwidth for PCIe storage tunneling.

Storage devices often become the bottleneck before the cable standard does. A SATA SSD behind a USB 3.2 Gen 2 enclosure is limited to around 550 MB/s by the SATA interface, well below the USB link speed. Only NVMe drives over USB or Thunderbolt can saturate modern high-speed connections.

This calculator accounts for all these factors, showing both the theoretical ceiling and a realistic estimate based on typical protocol overhead and common storage performance, so you can make informed decisions about which cable standard you actually need for your workflow.

FAQ

Why are real transfer speeds slower than advertised?
Advertised speeds are theoretical maximums measured at the physical layer. Real-world throughput is reduced by protocol overhead (USB headers, error correction), encoding schemes (8b/10b uses 20% of bandwidth), storage device speed limits, and driver or controller bottlenecks.
What is the fastest consumer cable standard?
Thunderbolt 5, announced with up to 80 Gbps bidirectional bandwidth and 120 Gbps in asymmetric mode, is the fastest. Thunderbolt 4 provides 40 Gbps. DisplayPort 2.1 with UHBR 20 reaches 80 Gbps for video, but is not a general data transfer standard.
How much faster is USB 3.2 than USB 2.0?
USB 3.2 Gen 2 offers 10 Gbps, which is roughly 20 times the 480 Mbps of USB 2.0. In practice the improvement is around 10-15 times because USB 2.0 rarely hits its theoretical maximum. USB 3.2 Gen 2x2 doubles this to 20 Gbps using two lanes.
Does cable quality affect transfer speed?
Yes. A poorly shielded cable or one with thin gauge wiring may not sustain the signaling rates required by high-speed standards. USB-IF certified cables and Thunderbolt certified cables are tested to guarantee full bandwidth. Cheap uncertified cables may fall back to slower speeds.
What is protocol overhead?
Protocol overhead is the portion of bandwidth consumed by packet headers, error correction codes, flow control signals, and encoding schemes rather than actual user data. For USB 3.x, typical overhead is around 10-20%. Ethernet overhead varies from about 3% for large frames to over 40% for small packets.