Megabits vs Megabytes
ISPs advertise megabits per second (Mbps). File sizes are often megabytes (MB). Divide Mbps by 8 for an approximate MB/s, then expect less in real transfers because of protocol overhead.
The factor of eight
1 byte = 8 bits, so 80 Mbps is theoretically 10 MB/s before overhead.
Decimal prefixes
SpeedTestLab uses SI decimal prefixes: 1 Mbps = 1,000,000 bits/s. Some operating systems still show MiB (1024-based) for files.
Worked example
A 1 GB file (1,000,000,000 bytes) at 100 Mbps has a theoretical time of 80 seconds. The calculator on this site uses that formula.
Frequently asked questions
Why is my download in MB/s smaller?
The browser or OS may show bytes. Also TCP, HTTP, and Wi‑Fi overhead consume part of the bit rate.
Is Gbps the same as GB/s?
No. 1 Gbps is about 125 MB/s theoretical.