How it's calculated
time (s) = (file size × 8) ÷ speed
file size in bytes (×8 converts to bits), speed in bits per second. Mbps/Gbps are decimal (×10⁶ / ×10⁹) while file sizes use binary KB/MB/GB (×1024). Real transfers run slower due to overhead.
Worked examples
| File size | Speed | Time | Note |
|---|---|---|---|
| 1 GB | 100 Mbps | 1 min 20 s | typical home fibre |
| 5 GB | 50 Mbps | 13 min 20 s | HD movie |
| 700 MB | 25 Mbps | 3 min 44 s | old CD-sized file |
| 50 GB | 1 Gbps | 6 min 40 s | game install |
Common questions
Why is the download slower than my plan promises?
ISPs advertise speed in megabits (Mbps) but browsers show megabytes (MB/s). There are 8 bits in a byte, so a 100 Mbps line tops out near 12.5 MB/s.
Will I actually hit my full speed?
Rarely. Server limits, Wi-Fi, and shared bandwidth mean real downloads usually run below the advertised figure, so treat the estimate as a best case.