Mbps vs MB/s: Why Downloads Look Slower Than Your Plan
The confusion in one sentence
Internet plans are sold in megabits per second (Mbps), but file sizes and download windows usually show megabytes per second (MB/s). There are 8 bits in a byte, so the MB/s number is one eighth of the Mbps number.
Converting between them
- Mbps to MB/s: divide by 8. A 100 Mbps plan peaks at about 12.5 MB/s.
- MB/s to Mbps: multiply by 8. A download showing 25 MB/s is using about 200 Mbps.
A quick feel for common plan speeds:
- 25 Mbps is about 3.1 MB/s.
- 100 Mbps is about 12.5 MB/s.
- 300 Mbps is about 37.5 MB/s.
- 1,000 Mbps (1 Gbps) is about 125 MB/s.
Case matters
Watch the letters. A lowercase b means bits and an uppercase B means bytes. Mbps and Mb/s are bits. MB/s is bytes. Storage is measured in bytes (GB and TB), while network speed is measured in bits.
How long downloads take
These times are the theoretical minimum for a file with 1 GB equal to 1,000 MB. Real downloads are slower, usually by 5 to 10 percent or more, because of overhead and busy servers.
1 GB (a short film or small game):
- 25 Mbps: about 5 minutes 20 seconds
- 100 Mbps: about 1 minute 20 seconds
- 300 Mbps: about 27 seconds
- 1,000 Mbps: about 8 seconds
5 GB (a game or software update):
- 25 Mbps: about 26 minutes 40 seconds
- 100 Mbps: about 6 minutes 40 seconds
- 300 Mbps: about 2 minutes 13 seconds
- 1,000 Mbps: about 40 seconds
50 GB (a large modern game):
- 25 Mbps: about 4 hours 27 minutes
- 100 Mbps: about 1 hour 7 minutes
- 300 Mbps: about 22 minutes
- 1,000 Mbps: about 6 minutes 40 seconds
The formula is: time in seconds = file size in gigabytes × 8,000 ÷ speed in Mbps.
Why you rarely see the full speed
- The server limits speed. A busy or distant server may send data more slowly than your line can take.
- Overhead. Every packet carries extra data for addressing, which takes a small share of the speed.
- Wi-Fi. Real Wi-Fi speeds are often well below the plan speed. See Wi-Fi vs Ethernet.
- Other devices. Everyone on the network shares the line.
- Your device. Slow storage or an old network adapter can cap speeds.
How to check your own line
Run the speed test on a cable with everything else paused. The number is in Mbps, so divide it by 8 to compare it with the MB/s figure a download window shows. If the two match, the line is doing its job.
Mbps and data caps
Data caps are measured in gigabytes, not in speed. A fast plan can burn through a cap quickly. At 100 Mbps a connection can move about 45 GB in an hour of full use, so a few hours of heavy downloads can use a large share of a monthly cap.