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.

What is the Bandwidth & Data Rate Reference?

Convert data transfer rates across bits and bytes per second — bps, Kbps, Mbps, Gbps, MB/s — and estimate download time for any file size, all in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Bandwidth & Data Rate Reference

Name: Bandwidth & Data Rate Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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.

Real-world reference: what different speeds feel like

Connection	Typical speed	Time to download 1 GB
Mobile 3G	~3 Mbps	~45 minutes
Mobile 4G	~30 Mbps	~4.5 minutes
Home broadband (entry)	~50 Mbps	~2.7 minutes
Home broadband (standard)	~200 Mbps	~40 seconds
Gigabit fibre	~1 Gbps	~8 seconds
10 Gbps data centre	~10 Gbps	~0.8 seconds

These are ideal-rate estimates. Actual transfers run slower due to protocol overhead, TCP slow-start, server limits, and congestion.

The decimal vs binary confusion

Network rates use SI (decimal) prefixes: 1 Mbps means exactly 1,000,000 bits per second. Storage capacity, on the other hand, is commonly reported in binary-based units where 1 MB can mean 1,048,576 bytes (a mebibyte) depending on the context. This is why copying a “1 MB” file might take slightly longer than your speed-test math suggests — the storage unit and the network unit are not the same size.

The tool here uses SI decimal prefixes throughout for network rates, which matches how ISPs advertise speeds and how speed-test sites report results.

Common mistakes to avoid

Confusing Mbps with MB/s: A 100 Mbps connection has a peak throughput of 12.5 MB/s, not 100 MB/s. Dividing by 8 is always the first step.

Ignoring overhead: TCP/IP, encryption (TLS), and application-level framing all consume a percentage of the raw link capacity. A practical rule of thumb is to expect 85–95% of the theoretical maximum on a clean wired connection, and often 60–80% on Wi-Fi or mobile.

Conflating link speed with server speed: A gigabit home connection cannot download faster than the server on the other end can serve. Many CDN-served files cap per-connection bandwidth deliberately; multiple parallel connections can help reach the full link speed in practice.