Bandwidth Calculator
How long to transfer a file?
For Bandwidth-Delay Product calculation
Common files
Common speeds
Transfer time
Theoretical
1m 25.9s
Real-world (95-70%)
1m 30.4s – 2m 2.7s
Theoretical assumes zero overhead. Protocol overhead, TCP slow start, congestion, and disk I/O typically limit real throughput to 70-95% of the theoretical maximum, so the transfer will likely take somewhat longer in practice.
| Seconds | 85.90 seconds | |
|---|---|---|
| Duration | 1 minute 25.9 seconds | |
| Hours | 0.0239 hours |
How it works
Transfer time is file size (in bytes) multiplied by 8 to get bits, divided by bandwidth (in bits per second): time = fileSizeBytes × 8 ÷ bandwidthBps. The ×8 matters because network bandwidth is measured in bits per second while file sizes are measured in bytes.
Bits vs bytes. ISPs advertise speed in Mbps (megabits), while file managers show size in MB (megabytes). A “100 Mbps” connection downloads at roughly 12.5 MB/s. This calculator handles the conversion automatically.
Binary vs decimal prefixes. File sizes use binary units (1 KB = 1024 bytes), matching how operating systems report file sizes. Bandwidth uses decimal units (1 Kbps = 1000 bps), matching IEEE and SI convention. This mismatch is standard industry practice, not an error.
Bandwidth-Delay Product. On a 1 Gbps link with 100ms round-trip time to a server across the ocean, 12.5 MB of data is simultaneously in transit. If the TCP receive window is smaller than this, the sender must pause and wait for acknowledgements, wasting bandwidth. TCP window scaling (RFC 7323) solves this and is enabled by default on modern operating systems, but sometimes needs manual tuning for high-BDP paths.
Real-world vs theoretical. This calculator shows the theoretical maximum. Actual throughput is reduced by protocol overhead (TCP/IP headers, roughly 3-5%), TCP slow start, congestion, packet loss, disk I/O, and shared links. A good rule of thumb: expect 70-95% of theoretical maximum under normal conditions. Read more inUnderstanding MTU, MSS, and Packet Fragmentation.
FAQ
How long does it take to transfer 1 TB at 1 Gbps?
Approximately 2 hours 26 minutes. 1 TB = 1,099,511,627,776 bytes = 8,796,093,022,208 bits. At 1 Gbps (1,000,000,000 bits/sec), that is about 8,796 seconds. Real-world throughput will be slightly lower due to protocol overhead and network conditions.
What is the difference between Mbps and MB/s?
Mbps (megabits per second) measures bandwidth in bits, used by ISPs and network specs. MB/s (megabytes per second) measures data rate in bytes, used by file managers and disk benchmarks. 1 MB/s = 8 Mbps. A 100 Mbps connection transfers at a theoretical maximum of 12.5 MB/s.
What is Bandwidth-Delay Product (BDP)?
BDP is the amount of data that can be "in the pipe" at any moment, calculated as bandwidth times round-trip time. For example, 1 Gbps x 100ms RTT = 12.5 MB. TCP needs a receive window at least this large to fully utilize the link. On high-latency links, BDP can be very large, requiring TCP window scaling.
Why is my actual transfer slower than my bandwidth suggests?
Several factors reduce real throughput: protocol overhead (TCP/IP headers consume roughly 3-5% of bandwidth), TCP slow start, congestion and packet loss, disk I/O speed, server-side limits, and shared bandwidth with other users. This calculator shows the theoretical maximum; real transfers typically achieve 70-95% of it.