File Transfer Calculator

Enter your total file size and sustained transfer speed to calculate transfer duration.

Estimated Transfer Time

11m 7s

100 GB at 150 MB/s

Total File Size 100.00 GB (800,000,000,000 bits)

Transfer Throughput 150.00 MB/s

Equivalent Bandwidth 1.20 Gbps (1,200 Mbps)

Convert MB/s to Mbps Download Calculator

How File Transfer Time is Calculated

Whether copying files to a USB thumb drive, moving footage to an external Thunderbolt SSD, or synchronizing backups across a 10GbE local NAS, transfer duration is determined by dividing total data volume by sustained transfer speed.

File Transfer Formula

Time (seconds) = (File Size in Bytes × 8) ÷ (Transfer Speed in bps × Efficiency)

Time Transfer Duration (seconds) — Total time required to copy or move the files across the medium
Size File Size (bytes / bits) — Total data volume to transfer across storage or network
Speed Transfer Speed (MB/s or Mbps) — Sustained throughput rate of your drive, USB bus, or LAN connection
Efficiency Transfer Efficiency (0 to 1) — Optional factor accounting for filesystem overhead or bus saturation

Example: 100 GB Backup to USB 3.0 External SSD at 150 MB/s

Transferring a 100 GB disk image or media catalog to an external USB 3.0 SATA SSD running at a sustained 150 MB/s write rate:

1
Convert File Size to Bytes and Bits 100 GB = 100,000,000,000 bytes × 8 = 800,000,000,000 bits (800 Gb) In decimal SI notation, 1 GB = 10⁹ bytes = 8 × 10⁹ bits.
2
Convert Transfer Speed to Bits per Second 150 MB/s = 150,000,000 bytes/s × 8 = 1,200,000,000 bits/s (1.2 Gbps)
3
Divide Total Bits by Transfer Speed 800,000,000,000 bits ÷ 1,200,000,000 bps = 666.67 seconds
4
Format Seconds into Human-Readable Duration 666.67 seconds = 11 minutes (660s) + 7 seconds Final estimated transfer time: 11m 7s.

Result Estimated transfer time: 11m 7s (or ~11m 42s with 5% filesystem overhead)

Storage & Hardware Transfer Speed Reference Table

Estimated transfer times for popular file sizes across common physical storage and local network interfaces:

Interface / Medium	Typical Speed	10 GB	50 GB	200 GB	1 TB
USB 2.0 Flash Drive	30 MB/s	5m 33s	27m 47s	1h 51m 7s	9h 15m 33s
1 GbE Local LAN / Wi-Fi 6	112 MB/s	1m 29s	7m 26s	29m 46s	2h 28m 49s
Mechanical HDD (USB 3.0)	140 MB/s	1m 11s	5m 57s	23m 49s	1h 59m 3s
SATA External SSD	450 MB/s	22s	1m 51s	7m 24s	37m 2s
10 GbE Local NAS Network	1,125 MB/s	9s	44s	2m 58s	14m 49s
NVMe USB-C / Thunderbolt 4	2,500 MB/s	4s	20s	1m 20s	6m 40s

Why Real-World Hardware Transfers Differ From Rated Speeds

Drive manufacturers advertise maximum burst read speeds, but sustained write operations are subject to real-world hardware dynamics:

SLC Cache Exhaustion: Solid-state drives cache initial writes in fast pseudo-SLC blocks. Once this buffer fills during large transfers, speeds drop to raw TLC/QLC NAND write levels.
Random vs Sequential File Transfers: Transferring single large video files achieves peak sequential bandwidth, whereas copying thousands of tiny files involves heavy random 4K I/O and directory metadata updates that can reduce speeds by 80% or more.
Thermal Throttling: High-speed NVMe and compact USB drives generate substantial heat. Under continuous heavy writes without active cooling, controllers reduce clock speeds to prevent overheating.
Filesystem & Protocol Overhead: Filesystem drivers (NTFS, APFS, exFAT, ext4) allocate block allocation tables, journal transactions, and checksum verification that consume measurable bus bandwidth.

Frequently Asked Questions

How do USB, SSD, and external drive speeds compare?

Standard USB 2.0 flash drives transfer at roughly 25–35 MB/s. Mechanical hard drives (HDDs) average 100–140 MB/s. USB 3.0/3.2 external SATA SSDs deliver 400–550 MB/s, while high-performance NVMe USB-C (Thunderbolt/USB4) drives exceed 1,000–2,800 MB/s.

Why do file transfers slow down halfway through?

Modern SSDs and flash drives use high-speed SLC cache buffers for initial write bursts. When transferring large files (e.g. 50 GB+), the SLC cache fills up, causing write speeds to drop to the native TLC/QLC NAND rate (often 50–150 MB/s). Thermal throttling can also reduce sustained speeds.

Why does transferring thousands of small files take longer than one large file?

Transferring thousands of small files (like source code or photo thumbnails) requires constant filesystem metadata updates, directory lookups, and random I/O operations, which drastically reduces throughput compared to sequential reading/writing of a single large archive or video.

How fast is a 1 Gbps or 10 Gbps local network (LAN) file transfer?

A standard Gigabit Ethernet (1 GbE) home network transfers files at a theoretical maximum of 125 MB/s (typically ~110–115 MB/s in real-world use). A 10 Gigabit (10 GbE) NAS connection can transfer up to 1,250 MB/s (1.12 GB/s) when paired with fast NVMe/SSD storage pools.