Download time calculator

The file is converted from megabytes to megabits (×8) and divided by the connection speed:

time (s) = size (MB) × 8 ÷ speed (Mbps)

The ×8 is the whole trick

Almost every frustration with internet speed comes down to two letters: lowercase b is bit; uppercase B is byte. And 1 byte = 8 bits.

Providers sell connections in Mbps (megabits per second). Files and download managers show MB (megabytes). So a 100 Mbps plan downloads, at best, 12.5 MB/s — not 100 MB/s. The provider is not cheating: these are different units.

To convert in your head: divide the plan speed by 8.

• 100 Mbps → 12.5 MB/s
• 300 Mbps → 37.5 MB/s
• 1 Gbps (1,000 Mbps) → 125 MB/s

Step by step (1 GB on a 100 Mbps plan)

1. Convert to megabytes: 1 GB = 1,024 MB
2. Convert to megabits: 1,024 × 8 = 8,192 Mb
3. Divide by the speed: 8,192 ÷ 100 = 81.9 s → about 1 min 22 s

Theoretical time by size and speed

File	50 Mbps	100 Mbps	300 Mbps	1 Gbps
100 MB (an app)	16 s	8 s	3 s	1 s
1 GB (a light movie)	2 min 44 s	1 min 22 s	27 s	8 s
5 GB (an HD movie)	13 min 39 s	6 min 50 s	2 min 17 s	41 s
50 GB (a big game)	2 h 16 min	1 h 8 min	22 min 45 s	6 min 50 s

Notice what the table says about upgrading your plan: going from 50 to 100 Mbps saves over an hour on the 50 GB game. Going from 300 Mbps to 1 Gbps saves 16 minutes. The gain per dollar collapses as speed rises — and above roughly 300 Mbps, your plan is rarely the bottleneck any more.

Why real downloads take longer

The number above is the theoretical ceiling. In practice, time is lost to:

• Protocol overhead — TCP/IP headers and retransmissions eat roughly 5% to 10% of the bandwidth. Not every transmitted bit is a bit of your file.
• The server at the other end — if it caps the rate per connection, your own speed becomes irrelevant. This is the most common reason a download crawls on a fast line.
• Wi-Fi — the contracted speed reaches the router, not necessarily the device. Walls, distance and neighbours on the same channel cut the rate; a cable removes that variable.
• The disk — on 1 Gbps connections an old mechanical drive can become the bottleneck instead of the internet.
• Sharing at home — bandwidth is split across every device, and peak hours affect the whole neighbourhood.

A reasonable rule of thumb: expect 80% to 90% of the theoretical time under good conditions, on a cable, with a server that does not throttle.

Is a GB 1,024 or 1,000 MB?

This calculator uses 1 GB = 1,024 MB, the binary convention shown by Windows and most file managers. Drive manufacturers use the decimal convention (1 GB = 1,000 MB) — which is why a "1 TB SSD" shows up as about 931 GB in the system. Neither is wrong; they are different rulers for the same thing.