Providers advertise speed in megabits per second (Mbps), while your browser shows file downloads in megabytes per second (MB/s). The difference is a factor of eight.
The rule
One byte has 8 bits, so MB/s = Mbps ÷ 8. A lowercase b means bit; an uppercase B means byte.
Conversion table
| Advertised (Mbps) | Max file download (MB/s) | About how long for 1 GB |
|---|---|---|
| 25 | 3.1 | 5 min 20 s |
| 50 | 6.25 | 2 min 40 s |
| 100 | 12.5 | 80 s |
| 200 | 25 | 40 s |
| 500 | 62.5 | 16 s |
| 1000 | 125 | 8 s |
Times are theoretical and approximate; real downloads are a little slower because of Wi‑Fi and server speed.
Bottom line
On a 100 Mbps plan, do not expect much more than about 12 MB/s. Run the speed test and compare your number with the table.