Bandwidth Calculator
File Transfer Time Estimation
Estimated Transfer Time
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Enter a file size and connection speed to estimate transfer time.
Understanding Bandwidth & Transfer Time
Bandwidth measures how much data a connection can move per second, usually advertised in decimal megabits (Mbps) by ISPs, while file sizes are typically shown in binary megabytes (MB) by operating systems. Mixing these units up is the most common reason a "100 Mbps" connection doesn't move a "100 MB" file in one second.
Bits vs. Bytes
Network speeds are measured in bits per second, while file sizes are measured in bytes. Since 1 byte = 8 bits, a 100 Mbps connection can move at most 12.5 MB per second under ideal conditions.
Protocol Overhead
Real-world transfers never hit the theoretical maximum. TCP/IP headers, encryption, Wi-Fi retransmissions, and network congestion typically eat 5-20% of available bandwidth.
Why Downloads Feel Slower Than Advertised
Your ISP plan lists the maximum theoretical throughput of the line itself, not what any single download will achieve. Shared network segments, the sending server's own upload capacity, and Wi-Fi signal quality all cap your real-world speed well below the advertised number.
Wired Beats Wireless
A wired Ethernet connection almost always delivers closer to the rated bandwidth than Wi-Fi, which loses throughput to interference and distance from the router.
Key Takeaways
- Divide by 8: To convert a connection's Mbps rating into MB/s, divide by roughly 8 (then subtract overhead).
- Overhead Adds Up: A 10-15% overhead estimate is realistic for most home internet and Wi-Fi transfers.
- Server-Side Limits: Your download can never exceed the sending server's own upload bandwidth, regardless of your connection speed.