Why is a 100 Mbps line not 100 MB/s?

Because Mbps means megabits per second and MB/s means megabytes per second, and a byte is 8 bits. A 100 Mbps connection delivers at most about 12.5 MB/s, before any protocol overhead.

What is the difference between bps and B/s?

bps is bits per second, the unit ISPs advertise. B/s (with a capital B) is bytes per second, what download managers usually show. Divide a bit rate by 8 to get the byte rate.

Are these units decimal or binary?

Network rates use decimal SI prefixes: 1 Kbps = 1000 bps, 1 Mbps = 1,000,000 bps. This differs from storage, where binary prefixes (1024-based) are common. This tool uses 1000-based prefixes throughout for rates.

Why is my real download slower than the calculated time?

The estimate assumes the full advertised rate with no overhead. Real transfers lose throughput to TCP/IP headers, latency, congestion, server limits and shared lines, so allow a margin above the ideal figure.

Does this run offline?

Yes. All conversions and the download estimate run locally in your browser. No data is uploaded, logged or stored.

Bandwidth & Data Rate Reference

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Bits, bytes, and how long a download takes

Network speeds are quoted in bits per second, but file sizes and download managers use bytes — a factor-of-8 difference that trips people up constantly. This reference converts between every common data-rate unit and estimates transfer time for any file size.

How it works

Every rate is converted to bits per second first, then out to each unit. Network prefixes are decimal (1000-based):

1 Kbps = 1000 bps          1 KB/s = 8000 bps
1 Mbps = 1,000,000 bps     1 MB/s = 8,000,000 bps
1 Gbps = 1,000,000,000 bps 1 GB/s = 8,000,000,000 bps

Download time is simply file size in bits divided by the rate in bits per second. A 100 MB file (800,000,000 bits) over a 100 Mbps line takes 800,000,000 / 100,000,000 = 8 seconds at the ideal rate.

Tips and notes

Divide an advertised Mbps figure by 8 to get the best-case MB/s you will see.
Network prefixes are decimal (1000); do not mix them with binary storage prefixes.
Real throughput runs below the advertised rate because of protocol overhead and latency.
For large transfers, latency matters less than sustained throughput — but a single slow hop caps the whole path.