Mbps vs MB/s: The Difference That Explains Your Slow Downloads
Your 100 Mbps plan delivers only 12.5 MB/s in real life. Here's exactly why, and how to read any internet speed you'll ever see.
By Piyush
If you have ever paid for a “100 Mbps” internet plan and then watched your browser report a download speed of around 12.5 MB/s, you are not being cheated by your ISP (well, not in this specific way). The two numbers use different units, and that is the source of basically every “why is my internet so slow?” question on the internet.
Bits and bytes: the actual difference
Every piece of digital information is made of bits. A bit is a single 0 or 1. Eight bits make a byte — enough to store a single character of text. When you see:
- Mbps — that is megabits per second
- MB/s — that is megabytes per second
The capital B means byte (8 bits). The lowercase b means bit. Multiply by 8 to go from bits to bytes. So:
100 Mbps ÷ 8 = 12.5 MB/s
Why your ISP advertises in Mbps
Internet service providers prefer the bigger-looking number. “100 Mbps” sounds more impressive than “12.5 MB/s”, even though they describe the same speed. It is also more accurate in a technical sense: the underlying transport of the internet (TCP/IP packets, ethernet frames) is measured in bits. Operating systems, browsers and download tools convert the speed into the more user-friendly bytes-per-second for display.
Real-world speeds
The table below shows what a few common plan speeds actually look like in a download tool:
- 10 Mbps → 1.25 MB/s
- 25 Mbps → 3.13 MB/s
- 50 Mbps → 6.25 MB/s
- 100 Mbps → 12.5 MB/s
- 500 Mbps → 62.5 MB/s
- 1 Gbps → 125 MB/s
Why you rarely get the full speed
Even when your plan says 100 Mbps, the speed you see in a downloader is usually 70–90% of the theoretical maximum. The reasons include:
- Protocol overhead — TCP/IP headers, TLS encryption and acknowledgements all eat a small slice of every connection.
- Server bottlenecks — the website or CDN serving the file might be slower than your connection.
- Wi-Fi quality — especially on 2.4 GHz or with walls between you and the router.
- Network congestion — evenings are usually slower because everyone is streaming.
How to use this in real life
A 100 Mbps connection is enough to stream 4K video (which only needs about 25 Mbps) and to download a 5 GB game in under 7 minutes. The huge numbers in fibre plans (300, 500, 1000 Mbps) really only matter if you have many devices using the network at once, or you regularly download multi-gigabyte files.
Convert any speed in seconds
Skip the mental math. Use the Mbps to MB/s converter to go from a plan speed to a real-world download speed, or the MB/s to Mbps converter for the reverse.
And if you want to know how long an actual download will take at your speed, the Download Time Calculator does the rest of the math for you.