Bandwidth / Transfer Time Calculator
Free data transfer time calculator. Work out how long a download or upload will take given a file size and connection speed.
Network speeds are decimal (1 Mbps = 1,000,000 bits/second, as ISPs advertise); file sizes are binary (1 GB = 1024 MB). Real-world transfers are usually slower than this due to protocol overhead.
Worked example
A 1 GB file over a 100 Mbps connection: 1 GB is 8,589,934,592 bits (1,024³ bytes × 8). At 100,000,000 bits per second, that's 8,589,934,592 ÷ 100,000,000 ≈ 85.9 seconds — about 1 minute 25 seconds, assuming the full connection speed is available for the whole transfer.
Frequently asked questions
Why is my download slower than my advertised internet speed?
The biggest reason is units: internet speeds are advertised in megabits per second (Mbps), but file sizes are shown in megabytes (MB) — and there are 8 bits in a byte. So a '100 Mbps' connection downloads at a theoretical maximum of 100 ÷ 8 = 12.5 MB per second, not 100 MB/s. On top of that, protocol overhead, other devices sharing the connection, Wi-Fi conditions, and the server's own upload speed all reduce real-world throughput further.
What is the difference between Mbps and MBps?
Mbps (megabits per second, lowercase 'b') is how connection speeds are normally advertised. MBps (megabytes per second, uppercase 'B') is how file sizes and download progress are normally shown. 1 MBps = 8 Mbps, so always check which one you're looking at before comparing numbers.
Why does this calculator use 1,024 for file size but 1,000 for speed?
File sizes (KB/MB/GB) follow the binary convention operating systems use for reporting file and storage sizes (1 KB = 1,024 bytes). Connection speeds (Kbps/Mbps/Gbps) follow the decimal convention networking equipment and ISPs use (1 Mbps = 1,000,000 bits per second) — mixing the two correctly is exactly what this calculator handles for you.