The single most common speed complaint on the internet — “I pay for 100 Mbps but only download at 12” — is a unit error, not a fault. Internet plans are sold in megabits per second (Mbps). Browsers, Steam, and download managers report megabytes per second (MB/s). One byte is eight bits, so the two numbers for the same connection differ by exactly 8× — and the ISPs, whose marketing prefers the bigger digit, are in no hurry to explain that.

The conversion, memorized once

Plan (megabits/s)	Theoretical (megabytes/s)	Realistic (~90%)
10 Mbps	1.25 MB/s	~1.1 MB/s
25 Mbps	3.1 MB/s	~2.8 MB/s
50 Mbps	6.25 MB/s	~5.6 MB/s
100 Mbps	12.5 MB/s	~11 MB/s
300 Mbps	37.5 MB/s	~34 MB/s
500 Mbps	62.5 MB/s	~56 MB/s
1,000 Mbps (gigabit)	125 MB/s	~110 MB/s

The “realistic” column exists because no transfer hits the theoretical line rate — TCP/IP and TLS headers, retransmissions and Wi-Fi losses take a steady cut, ~10% on a healthy link being a fair default. So a 100 Mbps test result means a good download shows ~11 MB/s, and a gigabit line shows ~110 MB/s, not 125.

Why it matters for picking a plan

Sizing bandwidth in MB/s-think leads to buying eight times too much or too little. If your mental model is “we download a lot of ~4 GB files,” the translation is: 4 GB ≈ 32 gigabits, which is ~6 minutes at 100 Mbps, ~1 minute at 500 Mbps. Run your household through the speed calculator with that unit straight, and the plan verdict lands on the right rung of the ladder.

When you need the real math

This page is the refresher. For the full treatment — the bit/byte/binary-unit rabbit hole, the transfer-time formula worked on real files, and a calculator that converts file size × speed into honest h/min/s including efficiency factors — our sibling site does exactly that: DownloadTime (the units explainer, the worked math). It’s the other half of the same question: this site sizes the pipe you need; that one times what flows through it.

Frequently asked questions

How do I convert Mbps to MB/s?

Divide by 8. One byte is eight bits, so 100 Mbps = 12.5 MB/s theoretical — and ~11 MB/s in practice after protocol overhead. Multiply MB/s by 8 to go the other way.

Why does my 200 Mbps plan only download at 25 MB/s?

Because 200 ÷ 8 = 25 — nothing is missing. The plan is measured in megabits, the download bar in megabytes. If you see ~22 MB/s instead of 25, the small gap is normal TCP/TLS overhead.

Is a gigabit connection 1,000 MB/s?

No — it's 1,000 megabits per second = 125 MB/s on paper, ~110–115 MB/s in real transfers. Still fast enough to pull a 50 GB game in about seven minutes.

What's the difference between MB and MiB?

A second split on top of the bit/byte one: MB is decimal (1,000 KB), MiB is binary (1,024 KiB) — a ~7% gap at the giga level. Some systems display GiB labeled as GB, which is why the same '50 GB' file can measure differently on different machines.

Do speed tests show Mbps or MB/s?

Mbps — same unit your ISP sells, deliberately. To translate a test result into 'how fast will Steam download,' divide by 8: a 300 Mbps test means ~37.5 MB/s peak.