Internet Download Time

Why it is 8,000 and not 1,024

Two different units are meeting. File sizes are quoted in bytes; connection speeds in bits per second. There are 8 bits in a byte, so 1 GB = 8 gigabits = 8,000 megabits (using the decimal definitions ISPs and drive makers sell with). The page multiplies gigabytes by 8,000 and divides by megabits per second.

This is why a "100 Mbps" line never delivers 100 MB/s. The theoretical ceiling is 12.5 MB/s, and most people see 10–11.5 MB/s on a good day.

Worked example

10 GB × 8,000 = 80,000 megabits. 80,000 ÷ 100 Mbps = 800 seconds = 13 minutes 20 seconds.

Halve the file to 5 GB at the same speed and it is 400 seconds. Keep 10 GB and move to a 500 Mbps line and it is 160 seconds, or 2 minutes 40 seconds.

Why the real download runs slower

• The server, not your line. Many hosts cap per-connection throughput well below your speed, so a fast line just waits faster.
• Wi-Fi. A 2.4 GHz link can cap out near 40–60 Mbps regardless of the plan; 5 GHz or Ethernet is needed to see the full figure.
• Overhead. TCP/IP headers, TLS and retransmissions consume a few percent. Protocol efficiency of 90–95% is normal.
• Contention. Cable and mobile plans share capacity with the neighbourhood, so evening speeds can be a fraction of the advertised peak.

Using it to choose a plan

Work backwards: a 50 GB game on a 100 Mbps line is about 67 minutes, on 500 Mbps about 13 minutes, on 1 Gbps about 7. If large downloads are rare, the difference rarely justifies the higher tier; if they are routine, the arithmetic above is the whole argument.

Common errors

• Entering megabytes per second where megabits are expected. A 100 MB/s fibre link entered as 100 returns a time about eight times too long — but the field label says Mbps for a reason.
• Comparing a Wi-Fi speed test with a wired plan. Test on Ethernet before concluding the line is slow.
• Forgetting that a "1 Gbps" plan is usually 940 Mbps after overhead, and often less over Wi-Fi.

Frequently Asked Questions