Download Time Calculator
Estimate how long a download takes from file size and connection speed — handling megabits vs megabytes correctly.
5 GB at 100 Mbps ≈ 400 seconds total (12.5 MB/s effective). Decimal (SI) units; ideal rate, before overhead.
To find download time, convert the file to bits (bytes × 8) and divide by the speed in bits per second. A 5 GB game is 40,000,000,000 bits; on a 100 Mbps line (100,000,000 bits/s) that is 400 seconds ≈ 6 min 40 sec. The ÷8 step matters because speeds are in megabits, files in megabytes.
Why 100 Mbps is not 100 MB/s
Internet plans are advertised in megabits per second (Mbps), but files are measured in megabytes (MB). A byte is 8 bits, so the two differ by a factor of 8. A 100 Mbps connection moves at most about 12.5 MB/s, which is why a “fast” plan can still feel slow when you watch the download counter tick over in megabytes. This calculator keeps the units straight: pick Mbps or Gbps when your speed is in bits, or MB/s when it is already in bytes, and it converts everything to bits before dividing.
Everything here uses decimal (SI) units, so 1 MB = 1000 KB = 1,000,000 bytes and 1 GB = 1,000,000,000 bytes. That matches how ISPs and file managers on macOS and Linux report sizes and speeds.
1 byte = 8 bits · convert MB→bytes (×1,000,000) then bytes→bits (×8) before dividing
Worked example: 5 GB on 100 Mbps
Convert the file to bits, convert the speed to bits per second, then divide.
- 1 Convert the file size to bytes. 5 GB × 1,000,000,000 = 5,000,000,000 bytes (decimal units).
- 2 Convert bytes to bits (× 8). 5,000,000,000 × 8 = 40,000,000,000 bits, because 1 byte = 8 bits.
- 3 Convert the speed to bits per second. 100 Mbps × 1,000,000 = 100,000,000 bits per second.
- 4 Divide bits by bits per second. 40,000,000,000 ÷ 100,000,000 = 400 seconds.
- 5 Express it as a readable duration. 400 seconds = 6 min 40 sec. This is the ideal time before overhead.
Megabits per second → megabytes per second
Divide Mbps by 8 for the maximum MB/s, then read a rough time for a 1 GB (1000 MB) file.
| Plan speed | Max MB/s (÷8) | Time for 1 GB |
|---|---|---|
| 25 Mbps | 3.125 MB/s | ≈ 5 min 20 sec |
| 50 Mbps | 6.25 MB/s | ≈ 2 min 40 sec |
| 100 Mbps | 12.5 MB/s | ≈ 1 min 20 sec |
| 500 Mbps | 62.5 MB/s | ≈ 16 sec |
| 1 Gbps | 125 MB/s | ≈ 8 sec |
Why real downloads run slower than this
The number here is a best case: file size in bits divided by the raw link speed. Real transfers rarely hit it. Protocol overhead (TCP/IP and TLS headers, acknowledgements, retransmissions) skims a few percent off the top. The server or CDN may cap your rate, throttle after a burst, or be busy. Wi-Fi, powerline adapters, and shared household connections all lose speed to interference and congestion. Disk write speed can also become the bottleneck on very fast links. Treat this estimate as the ceiling and expect the actual time to land somewhat above it.