How long to download 100 GB at 10 Mbps

Eighty thousand seconds, and where each part comes from

One hundred gigabytes at 10 Mbps takes 80,000 seconds. That is 22 hours 13 minutes 20 seconds, or 22.222 hours, or 1,333.3 minutes. Every figure on this page comes from one chain. One hundred GB is 100,000 MB, each MB is 8 megabits, so the payload is 800,000 megabits, and a 10 Mbps line delivers 10 megabits every second.

The byte side is shorter to read. Ten megabits per second is 1.25 MB/s, because eight bits make one byte. A minute at that rate moves 75 MB. An hour moves 4,500 MB, which is 4.5 GB. One gigabyte costs 800 seconds, and 800 seconds is 13 minutes 20 seconds.

The prefix here is decimal. Giga means 10^9 in the International System of Units, as the NIST table of metric prefixes sets out, so a gigabyte is 1,000,000,000 bytes and a megabyte is 1,000,000. That is why the chain multiplies by 8,000 rather than 8,192.

Overhead is the only correction most readers need. Add 3 percent and 80,000 seconds becomes 82,400 seconds, or 22 hours 53 minutes 20 seconds. The size of the file and the rate of the plan never move.

Almost every start hour pushes the finish into the next day

A 22 hour job fits inside a single 24 hour window, with 6,400 seconds left over. That leftover is 1 hour 46 minutes 40 seconds. The wall clock is the awkward part: press start at 8:00 am and the file lands at 6:13:20 am the next morning.

Only a start before 1:46:40 am finishes on the same calendar day, since that is the exact margin left in the window. Everything later rolls over, and a Monday morning start finishes on Tuesday. A Friday evening start finishes on Saturday afternoon, which is often the better plan for a home connection that other people share in the evening.

Overhead moves the finish rather than the day count. At 3 percent the same 8:00 am start lands at 6:53:20 am, because 82,400 seconds is 22 hours 53 minutes 20 seconds. At 10 percent the job needs 88,000 seconds, which is 24 hours 26 minutes 40 seconds, and no single day can hold it. That start finishes at 8:26:40 am on the following morning with 1,600 seconds of the second day already spent.

One gigabyte costs 13 minutes 20 seconds

With the rate fixed at 10 Mbps, time scales with size and nothing else. Each gigabyte is 800 seconds, so the arithmetic for any other file is one multiplication. Ten gigabytes is 8,000 seconds, or 2 hours 13 minutes 20 seconds. Fifty gigabytes is 40,000 seconds, 11 hours 6 minutes 40 seconds. Two hundred fifty gigabytes is 200,000 seconds, 55 hours 33 minutes 20 seconds.

Turned around, the rate gives a daily budget. One full day of wire time is 86,400 seconds, and at 800 seconds a gigabyte that is 108 GB of payload. Two days carry 216 GB, which is a little over two copies of this file. A week carries 756 GB, close to the size of a small external drive.

That budget is what makes a 100 GB transfer on 10 Mbps a planning problem rather than a waiting problem. Twenty-two hours is 13 percent of all the hours in a week, so a household that pulls one file this size every week spends an eighth of its clock on downloads alone. Two of them in the same week, and the line is busy for a quarter of the time.

1.25 MB/s is a trickle that no disk or router will notice

The disk is never the limit at this rate. Writing 100 GB to a 7,200 rpm drive at 120 MB/s takes 833 seconds, or 13 minutes 53 seconds. A SATA solid state drive at 500 MB/s needs 200 seconds, 3 minutes 20 seconds. A slow USB 2.0 stick at 30 MB/s needs 3,333 seconds, 55 minutes 33 seconds, and even that is 24 times faster than the line.

The router has the same kind of headroom. An 802.11n router on the 2.4 GHz band delivers 40 to 70 Mbps to a laptop in the next room, which is four to seven times what the line asks for. A router from the last decade can carry 10 Mbps without strain, and a wired port can carry a hundred times that.

Context explains why the number feels small. The FCC broadband speed guide sets out what common household activities need in megabits per second, and the federal fixed benchmark has been 100 Mbps down and 20 Mbps up since 2024. A 10 Mbps line runs at a tenth of that floor, so the file takes ten times as long as the same file on a current entry plan.

Wi-Fi and the server can each take the finish away from the line

The plan is measured at the modem. A laptop on 5 GHz in the same room sees 85 to 95 percent of the label, and two walls away it sees 55 to 70 percent. At 85 percent the line delivers 8.5 Mbps and the file needs 94,118 seconds, or 26 hours 8 minutes 38 seconds, which is 3 hours 55 minutes 18 seconds longer. At 70 percent it needs 114,286 seconds, 31 hours 44 minutes 46 seconds, and the job is 9 hours 31 minutes 26 seconds late.

Server caps bite less often at this rate, but they bite harder when they do. A mirror that limits one connection to 1 MB/s, which is 8 Mbps, needs 100,000 seconds, 27 hours 46 minutes 40 seconds, and leaves 20 percent of the line idle the whole time. A cap of 1.1 MB/s still costs 10,909 seconds, and a cap of 2 MB/s never binds because it sits above the line.

The 2.4 GHz band is the usual culprit. It carries 40 to 70 Mbps in a quiet house and falls to 20 Mbps when the neighborhood is busy, so a wireless hop can lose more than half of a slow line at the worst hour of the evening. The FCC home network tips put the tradeoff plainly: 5 GHz is faster and covers less distance. On a 22 hour transfer, an Ethernet cable removes the variable for good.

Overhead and the GiB reading together add 1 hour 38 minutes

Two corrections sit between the clean answer and the time a real client reports. The first is protocol and retransmission overhead, and the second is the unit a file manager uses. Both have a formula, so neither needs guessing.

Seconds = (gigabytes x 8,000 x (1 + overhead / 100)) / Mbps. For this file at 3 percent that is (100 x 8,000 x 1.03) / 10 = 82,400 seconds. At 6 percent it is 84,800 seconds, or 23 hours 33 minutes 20 seconds. At 10 percent it is 88,000 seconds, 24 hours 26 minutes 40 seconds, which is the point where the transfer stops fitting in a day.

The unit is the larger surprise. A 100 GiB file is 107,374,182,400 bytes, which is 107.3741824 decimal GB, so the payload is 858,993 megabits and the line needs 85,899 seconds. That is 23 hours 51 minutes 39 seconds, and the gap against the decimal answer is 5,899 seconds, or 1 hour 38 minutes 19 seconds. Windows reports sizes in GiB and labels them GB, which is where the confusion starts.

Read the last row as the honest worst case. A transfer manager that shows 100 GB, a disk that counts in GiB and a line with normal overhead land at 24 hours 34 minutes 36 seconds. That is more than a day, and it is the number to plan around when a deadline is involved.

A 100 GB file is 8 percent of a 1.2 TB monthly cap

Data allowances are quoted in decimal terabytes, so 1.2 TB is 1,200 GB. One file is 8.33 percent of that, exactly one twelfth. At 4.5 GB an hour the whole allowance takes 266.7 hours of flat out transfer, or 11.1 days of downloading around the clock.

Three files in a month take 300 GB, a quarter of the 1.2 TB allowance. Add a few game updates at 20 to 50 GB each and the allowance is half gone before any streaming is counted. That is the practical argument for scheduling this transfer at the start of a billing cycle rather than the end.

A failed transfer is the expensive case on a metered plan, because the bytes are charged even when the file never finishes. A client that restarts from zero after 80 percent has already paid for 80 GB and throws away 64,000 seconds of line time, which is 17 hours 46 minutes 40 seconds. Resume support and a checksum at the end turn that failure into a short delay instead of a wasted day.

Seven checks before a 22 hour transfer starts

A transfer this long is decided before it starts. Each check below takes a minute and removes a way for the line to waste the day.

1. Free space. Plan for 110 GB, the file plus 10 percent for the temporary copy and the log.
2. Use a cable. Ethernet for the whole run if the router is within reach, otherwise 5 GHz close to it.
3. Pick a client that resumes. A partial file plus a checksum means a dropped connection costs minutes, not 22 hours.
4. Turn off sleep. A laptop that naps after 30 minutes can stall the job even while the disk keeps writing.
5. Choose the start hour. An 8:00 am start finishes at 6:13:20 am the next day, so the family evening stays free.
6. Read the counter at 5,000 MB. That should appear after 4,000 seconds, 1 hour 6 minutes 40 seconds. If it takes twice as long, the connection is running at half rate.
7. Verify the hash. Hashing 100 GB at 500 MB/s takes 200 seconds. At 120 MB/s it takes 833 seconds.

None of these steps makes the line faster. They stop the transfer from losing speed it already has, which on this file is worth more than any router upgrade. A 100 GB download on 10 Mbps is a 22 hour event, and the only real shortcut is a faster plan.