How long to download 100 GB at 50 Mbps

Half a morning, and the three divisions that produce it

One hundred decimal gigabytes is 800,000 megabits. At 50 Mbps that is 16,000 seconds, because 50 goes into 800,000 sixteen thousand times. Read the same number in minutes and it is 266.67, and in hours it is 4.4444.

The byte side is the one that shows on a download meter. Fifty megabits a second is 6.25 MB/s, since eight bits make a byte. A minute at that rate moves 375 MB, an hour moves 22,500 MB, and one gigabyte costs 160 seconds, which is 2 minutes 40 seconds.

The units are decimal, so a gigabyte is a thousand megabytes and a megabyte is a thousand kilobytes, as the NIST prefix chart shows. A file manager that reports 100 GiB is describing 107.3741824 decimal GB, and that file needs 17,180 seconds, 4 hours 46 minutes 20 seconds, which is 19 minutes 40 seconds more than the clean answer.

The counter should read 25 GB by 10:06:40

A four and a half hour job is long enough that you can check it, and short enough that a check is worth doing. Split the file into quarters and each one takes 4,000 seconds. Start at 9:00 am and the counter should pass 25 GB at 10:06:40, 50 GB at 11:13:20, 75 GB at 12:20:00, and 100 GB at 1:26:40 pm.

Overhead shifts every mark by the same 480 seconds at 3 percent. The job becomes 16,480 seconds, or 4 hours 34 minutes 40 seconds, and the last byte lands at 1:34:40 pm. At 10 percent the total is 17,600 seconds, 4 hours 53 minutes 20 seconds, and the finish is 1:53:20 pm.

That still leaves the afternoon. A 9:00 am start is the useful default for a file this size: it uses the morning, finishes before the 2 pm meeting, and does not sit in the evening when the house wants the line for video.

One 4K stream takes 15 Mbps and leaves 35

Streaming is the usual competition. Netflix recommends 15 Mbps or more for 4K, and the Netflix speed table puts 1080p at 5 Mbps and 720p at 3 Mbps. A 50 Mbps line with one 4K stream left has 35 Mbps, so the file needs 22,857 seconds, which is 6 hours 20 minutes 57 seconds.

Add an HD video call at 6 Mbps and 29 Mbps remain. The same file now takes 27,586 seconds, 7 hours 39 minutes 46 seconds, which is 3 hours 13 minutes 6 seconds more than an empty line. The workday is gone, and the file is still running at dinner.

The last row is the one that surprises people. Three 4K sets on a 50 Mbps plan leave 5 Mbps, which is the bottom of the range the FCC lists for a single HD stream, and the download stretches to 44 hours 26 minutes 40 seconds.

The FCC guide to home use draws the line at 25 Mbps: 12 to 25 is the middle group, and anything above 25 is advanced. A 50 Mbps plan belongs to the top group, but only while fewer than three 4K streams are running.

The drive keeps up, the unpacking may not

The line delivers 6.25 MB/s, so any drive that writes faster than that never becomes the bottleneck. A 3.5 inch hard drive at 120 MB/s writes the whole 100 GB in 833 seconds, 13 minutes 53 seconds. A SATA solid state drive at 500 MB/s needs 200 seconds. Even a slow USB 2.0 stick at 30 MB/s finishes writing in 3,333 seconds, 55 minutes 33 seconds, and the download is still running.

The work after the download is what people forget. A game client that unpacks a compressed depot, rebuilds the archive and checks every chunk against a manifest at 100 MB/s spends another 1,000 seconds, 16 minutes 40 seconds, after the last byte arrives, so a clean 9:00 am start hands over a playable install at 1:43:20 pm, and the panel shows 1:51:20 pm once 3 percent overhead is counted. A client that reads the file back to check a hash at 250 MB/s adds 400 seconds.

Do both and the real elapsed time is 17,400 seconds, 4 hours 50 minutes, not 4 hours 26 minutes 40 seconds. That is 23 minutes 20 seconds of housekeeping, and it is the difference between a file that is ready when the counter hits zero and a file that is ready a little later.

One file is 8.3 percent of a 1.2 TB month

Data allowances are sold in decimal terabytes, so 1.2 TB is 1,200 GB. One 100 GB file is 8.33 percent of that, which is one twelfth. Twelve files of this size would use the whole allowance, and at 22.5 GB an hour the transfer time to fill it is 53 hours 20 minutes.

Providers meter the bytes at the modem rather than at the screen, so a retry after a failed transfer is billed a second time. A stuck job that loops three times can spend 300 GB without producing a usable file.

Two files a month is 16.7 percent, which most households never notice. The cap only becomes a planning problem when a console, a phone backup and a work laptop share the same allowance, and that is when the timing of this download starts to matter.

One more cost sits on a metered plan: a failed transfer is charged even when the file never finishes. A job that dies at 80 percent has already pulled 80 GB, and a client without resume will pull it again.

What the next 50 Mbps would buy

Doubling the plan halves the wait, and the saving is easy to state. At 100 Mbps the file takes 8,000 seconds, 2 hours 13 minutes 20 seconds, which is 2 hours 13 minutes 20 seconds less than this line. A gigabit plan needs 800 seconds, 13 minutes 20 seconds.

The gains shrink as the rate climbs. Going from 10 to 50 Mbps removes 17 hours 46 minutes 40 seconds from this job. Going from 50 to 100 Mbps removes 2 hours 13 minutes 20 seconds. Going from 500 Mbps to 1 Gbps removes 13 minutes 20 seconds, which is less than the time it takes to find the cable.

That is the argument for 50 Mbps as a middle tier. It turns a download that needs a night into one that needs a morning, and it does so without asking the household to stop streaming while it runs.

Ten minutes in, the counter tells you the truth

You do not have to wait four hours to learn whether the job will finish on time. Ten minutes is 600 seconds, and at 6.25 MB/s that is 3,750 MB, or 3.75 GB. Read the counter at that point and divide by 600 to get the rate in MB/s, then multiply by 8 for Mbps.

A reading of 1.875 GB does not mean the plan is broken. It usually means a device is streaming, the laptop is on 2.4 GHz in another room, or the server is capping the connection. Those three causes cover most slow downloads, and each one shows up in the first ten minutes rather than at hour three.

If the counter shows 1.25 GB and the deadline is lunch, stop the job. Restarting at 9:10 am costs ten minutes. Discovering the problem at 1:30 pm costs the afternoon, and the file still is not done.