Data Storage and Transfer Time Calculator

What this calculator answers

Three questions about digital data, in one place. Sizes converts between bits, bytes and the decimal (kB, MB, GB, TB, PB) and binary (KiB, MiB, GiB, TiB, PiB) units, and shows your size in both systems side by side. Speeds converts internet speeds such as Mbps into MB/s and shows how much a steady speed moves in an hour, a day or 30 days. Transfer time works out how long a file takes to download or upload at a given speed, or how fast a connection must be to move it in time.

How to use it

• Convert or estimate: pick the tool. Each keeps its own values, so you can switch back and forth.
• Sizes: type the Data size, then choose From and To. Units with an “i” (KiB, MiB, GiB, TiB, PiB) are binary and step by 1,024; the others step by 1,000. Significant figures trims long results; Auto keeps up to 12 figures but writes whole numbers out in full. Under the result, every byte unit also has a box of its own: type into any of them (say 500 in the MiB box) and that unit becomes From, while the other boxes follow.
• Speeds: type the Data rate and choose its units. Internet speeds are quoted in megabits per second (Mbps), so start there if you are converting a plan’s speed.
• Transfer time: choose whether to Find the time or the speed needed. Enter the File size with its unit, then the Connection speed (for the time) or the Time available (for the speed), written like 10 min, 2 h or 1:30. Overhead is optional: the percentage of the connection that carries something other than your file. Leave it empty for the best case.

The Try buttons load a file-size conversion, a plan speed in MB/s, a game download and a deadline, each worked through below. Under a size or speed result, a button carries that value into the transfer tool. Under a transfer time, Continue in the Time Duration Calculator carries the time into that calculator’s clock-time mode: enter the time you start, and it gives the time the transfer finishes.

How many MB are in a GB: 1,000 or 1,024?

1,000. A gigabyte (GB) is 10⁹ bytes and a megabyte (MB) is 10⁶ bytes, because kilo, mega and giga are the SI prefixes for powers of ten. The 1,024 belongs to the binary units: a gibibyte (GiB) is 1,024 mebibytes (MiB), or 2³⁰ bytes.

So 3,500 MB is exactly 3.5 GB (the 3,500 MB to GB button). The same 3,500,000,000 bytes divided by 1,073,741,824 come to about 3.26 GiB.

The last column is how much smaller the number gets when the same bytes are counted in the binary unit of that row: 1 − 1000ⁿ ÷ 1024ⁿ at the nth prefix. The gap grows with every step, so it is small for kilobytes and over a tenth for petabytes.

GB vs GiB: decimal and binary prefixes

Both count bytes; they differ only in the step between units. Computer professionals began using “kilo” for 1,024 because 2¹⁰ is close to 1,000, and the habit spread to mega and giga. To end the double meaning, the International Electrotechnical Commission (IEC) approved separate binary prefixes in December 1998: kibi (Ki), mebi (Mi), gibi (Gi), tebi (Ti) and pebi (Pi). They are not part of the SI, and kilo, mega and giga keep their decimal meaning.

The old habit survives in places. NIST notes that computer memory makers mostly use binary megabytes while storage makers mean 10⁶ bytes, and that telecommunications engineers use a megabit per second for 10⁶ bits per second. So one label, “GB”, can mean two amounts. This calculator writes GB only for 10⁹ bytes and GiB for 2³⁰ bytes.

To convert a size, multiply by the bytes in the From unit and divide by the bytes in the To unit:

• $x_{\text{from}}$ is your number and $x_{\text{to}}$ the same size in the new unit.
• $b_{\text{from}}$ and $b_{\text{to}}$ are the bytes in one of each unit: 10⁹ for GB, 2³⁰ for GiB, 1/8 for a bit.

Why a 1 TB drive shows about 931 GB

Because the drive is labeled in decimal units and some software counts it in binary units. Storage makers count 1 TB as one trillion bytes. Software that divides by 1,024 at each step, but still writes “GB”, shows the same trillion bytes as about 931 GB. Apple, for example, says iOS 10 and earlier and OS X Leopard and earlier reported sizes this way.

Worked example: a 1 TB drive in gibibytes (the calculator’s first view):

1. 1 TB = 10¹² = 1,000,000,000,000 bytes.
2. 1 GiB = 2³⁰ = 1,073,741,824 bytes.
3. 1,000,000,000,000 ÷ 1,073,741,824 = 931.322574615 GiB.
4. In tebibytes: 1,000,000,000,000 ÷ 2⁴⁰ = 0.909494701773 TiB, which is why the same drive can appear as “0.91 TB”.

No bytes are missing: the unit is 7.37% bigger, so the number is 6.87% smaller. The free space you see is lower again, because formatting and the operating system take part of the drive.

Bits vs bytes: Mbps vs MB/s

Divide megabits per second by 8 to get megabytes per second, because a byte is 8 bits. Internet speeds are quoted in megabits per second (Mbps), while file sizes are counted in bytes. The calculator writes bits as “bit” (Mbit/s) and bytes as “B” (MB/s), and shows a note if you enter a connection speed in bytes per second.

For a 100 Mbps plan (the 100 Mbps to MB/s button):

1. 100 Mbps = 100,000,000 bits per second.
2. 100,000,000 ÷ 8 = 12,500,000 bytes per second = 12.5 MB/s.
3. In binary units: 12,500,000 ÷ 1,048,576 = about 11.92 MiB/s.
4. Held for an hour: 12,500,000 bytes × 3,600 s = 45,000,000,000 bytes, or 45 GB.

How long will a download take?

Turn the file size into bits and divide by the part of the speed that carries the file:

• $t$ is the time in seconds and $S$ the file size in bytes (10⁹ per GB, 2³⁰ per GiB).
• $R$ is the connection speed in bits per second (10⁶ per Mbps).
• $o$ is the overhead as a decimal (10% = 0.1); 0 gives the best case.

Worked example: an 80 GB download on a 250 Mbps plan (the 80 GB at 250 Mbps button, which shows the 10% case beside the best case):

1. 80 GB = 80,000,000,000 bytes × 8 = 640,000,000,000 bits.
2. 250 Mbps = 250,000,000 bits per second.
3. Best case: 640,000,000,000 ÷ 250,000,000 = 2,560 seconds = 0:42:40.
4. With 10% overhead, 250,000,000 × 0.9 = 225,000,000 bits per second carry the file, and 640,000,000,000 ÷ 225,000,000 = 2,844.44 seconds = 0:47:24.
5. That effective 225 Mbit/s is 28.125 MB/s, the figure a download manager counting in decimal units would show.

Under the result, a table repeats the same file at speeds from 5 Mbps to 10 Gbps, with your own speed marked.

How fast a connection do you need?

Divide the bits by the seconds you have, then allow for overhead. For 20 GB in 10 minutes (the 20 GB in 10 min button):

1. 20 GB = 160,000,000,000 bits, and 10 minutes = 600 seconds.
2. 160,000,000,000 ÷ 600 = 266,666,667 bits per second = 266.67 Mbps, or 33.333 MB/s.
3. With 10% overhead: 266.67 ÷ 0.9 = 296.3 Mbps.

The table under this result gives the speed needed for time limits from 1 minute to 1 day.

Why real transfers are slower than the estimate

The estimate assumes every bit of the speed carries your file for the whole transfer. Real connections spend some bits on addressing and control. On an Ethernet network an IP packet holds at most 1,500 bytes; a typical IPv4 header takes 20 of them and a TCP header without options another 20. That leaves at most 1,460 bytes of file per packet, so 40 ÷ 1,500 = 2.67% goes to headers before Ethernet framing, TCP options or resent packets add more.

Other limits sit outside the formula. Everything else using the connection at the same time shares its speed; the FCC’s speed guide gives its figures for one activity at a time. A transfer also goes no faster than the slowest link between the two ends, which may be the server or your Wi-Fi rather than your plan. For a realistic estimate, enter a measured speed from a speed test and an overhead for the margin you want (headers alone take at least 2.67% of each full packet), then compare it with the best case the result shows beside it.

Reading the result

• Sizes: the headline is your size in the To unit, marked exact or rounded, with the factor both ways. The tiles give the size in bytes and in the best-fitting decimal and binary unit; the binary tile says how software that counts in 1,024s would label it. The boxes put every decimal unit beside its binary partner (kB beside KiB, GB beside GiB), so the gap at each prefix level is in plain view; the table below them adds the bit units (bit to Tbit), marks each value exact or rounded, and a unit name there makes it the main result.
• Speeds: the headline gives the rate in the To unit, and the tiles show how much it moves per hour, per day and per 30 days, in decimal and binary units.
• Transfer time: the headline is h:mm:ss, or days, hours and minutes for transfers over a day. The tiles give the effective speed after overhead, the time per gigabyte and the same transfer with no overhead (or with 10% if you entered none). The steps show each unit change.

Assumptions and limitations

• Decimal units mean powers of 1,000 and binary units powers of 1,024; a byte is 8 bits. Converted values are exact rational results rounded once for display.
• A transfer runs at one steady speed from start to finish. Real speeds rise and fall, and the calculator does not model compression, connection setup, or the time to unpack or install a file after it arrives.
• Overhead is one percentage for everything that is not your file: headers, resent data and other traffic.
• The 30-day figure in Speeds uses 30 days of 24 hours.
• Converting a drive’s size does not predict its free space: formatting, the operating system and your files use part of it.

Common mistakes

• Entering a plan’s Mbps as MB/s. 100 MB/s is 800 Mbit/s, so a 50 GB file would seem to take 500 seconds (0:08:20) instead of 4,000 seconds (1:06:40).
• Mixing GB and GiB in one sum. 50 GiB is 53.687 GB, so a file that software lists as “50 GB” in binary units takes 7.37% longer to move than a true 50 GB file.
• Using 1,024 for network speeds. Network speeds use decimal prefixes, so a megabit per second means 1,000,000 bits each second, not 1,048,576.
• Expecting the plan’s full speed. The plan speed is a ceiling. Estimate with a measured speed and some overhead, and treat the best case as the fastest possible time.