Data Transfer Calculator
A 10 GB file over a 100 Mbps connection takes about 13 minutes and 20 seconds in theory. A data transfer calculator works out that kind of estimate by solving for whichever value you do not already know: transfer time, transfer speed, or data size. Enter any two of the three and the tool computes the third using consistent bit and byte conversions. This is useful when you are planning a file upload, sizing a backup window, checking whether an internet plan can move a video project before a deadline, or figuring out how long a cloud sync will realistically take. The calculator supports both decimal size units (KB, MB, GB, TB) and binary size units (KiB, MiB, GiB, TiB), plus common network speed units (Kbps, Mbps, Gbps), so the numbers match whatever your operating system, router, or ISP happens to display.
Quick answer
Pick a solve mode: time, speed, or size, based on which value you don't already have.
What this tells you
- •Pick a solve mode: time, speed, or size, based on which value you don't already have.
- •The calculator converts everything to bits and bytes internally before doing any math, since network speeds are measured in bits per second while file sizes are measured in bytes.
- •Decimal units (GB, TB) use powers of 1000, while binary units (GiB, TiB) use powers of 1024. The two are close but not identical, and the gap grows at larger sizes.
- •Results are theoretical maximums based on the numbers you enter. Real-world transfers are almost always slower because of overhead, congestion, and hardware limits.
- •The headline of the result is the value you solved for, in the unit you picked: the duration in Time mode, the required speed in Speed mode, and the data volume in Size mode. The lines below repeat size, speed, and time together.
How to Use
- 1Choose what you want to solve for in the Solve for field: Time, Speed, or Size. This tells the calculator which of the three inputs to compute and which two to treat as known values.
- 2Enter the data size and select its unit. Use GB or MB for most files, or switch to GiB or MiB if your operating system reports size in binary units (Windows File Explorer typically does).
- 3Enter the transfer speed and select its unit (Kbps, Mbps, or Gbps). This should match the number your ISP, router, or network adapter reports, which is almost always in bits per second, not bytes.
- 4Enter the transfer time and select its unit (seconds, minutes, or hours) if time is one of your known values.
- 5Click Calculate. The headline shows the answer for the mode you chose: the transfer time, the required speed in your speed unit, or the data volume in your data unit. The lines below list all three values, with the time also in seconds.
How It Works
Formula
Bits = Bytes x 8
Time (seconds) = (Size in bytes x 8) / Speed in bits per second
Speed (bps) = (Size in bytes x 8) / Time in seconds
Size (bytes) = (Speed in bps x Time in seconds) / 8File and storage sizes are measured in bytes, but network speeds are measured in bits per second, and there are 8 bits in a byte. The calculator first converts your size input to bytes and your speed input to bits per second using standard unit factors, then multiplies the byte count by 8 to get bits before solving for whichever variable you asked for. Decimal units (KB, MB, GB, TB) scale by 1000 per step, matching how storage manufacturers and most speed test tools label sizes. Binary units (KiB, MiB, GiB, TiB) scale by 1024 per step, matching how operating systems like Windows often report file and drive sizes internally. Mixing the two without noticing is one of the most common sources of a 'why doesn't this match' moment, which is why the calculator keeps them as separate, explicit unit choices instead of guessing.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
How long to upload a 10 GB video file
10 GB converts to 10,000,000,000 bytes, which is 80,000,000,000 bits. Dividing by a speed of 100,000,000 bits per second gives 800 seconds. This is the theoretical minimum time at a steady, uninterrupted 100 Mbps, before accounting for overhead or network variance.
Minimum upload speed to back up a DVD image before a deadline
A 4.7 GB DVD image is 4,700,000,000 bytes, or 37,600,000,000 bits. With a 600-second window (10 minutes), the required speed works out to roughly 62,666,667 bits per second, which the calculator shows as 62.6667 Mbps. Any connection rated below that will not finish in time even under ideal conditions.
How much data a gigabit connection can move in an hour
A 1000 Mbps (1 Gbps) connection sustained for 3,600 seconds moves 3,600,000,000,000 bits, which is 450,000,000,000 bytes, or 450 GB. This is a theoretical ceiling. Real gigabit connections rarely sustain the full rated speed for a full hour due to overhead and other network activity.
Transfer time using a binary size unit
500 MiB equals 524,288,000 bytes because binary units scale by 1024, not 1000. Converted to bits (4,194,304,000) and divided by a speed of 20,000,000 bits per second gives about 209.72 seconds, which rounds to 3 minutes and 30 seconds. Using 500 MB instead of 500 MiB here gives 200 seconds, or 0h 3m 20s, so the binary unit adds about 10 seconds.
Estimated time to back up a 2 TB drive over USB 3.0
2 TB is 2,000,000,000,000 bytes, or 16,000,000,000,000 bits. At the USB 3.0 signaling rate of 5 Gbps (5,000,000,000 bits per second), that works out to 3,200 seconds, or 53 minutes and 20 seconds. USB 3.0, now called USB 3.2 Gen 1, sends 10 bits on the wire for every 8 bits of data, so only 4 Gbps carries the file, and a second run at 4 Gbps gives 4,000 seconds before any protocol overhead. Real USB 3.0 transfers to spinning or external drives are usually well below even that because the drive's own read and write speed becomes the actual bottleneck, not the cable.
Scenario: Marco moves a video archive to a new NAS overnight
Marco has a 1.8 TB folder of client video to move from his workstation to a new NAS over gigabit Ethernet. The nightly backup holds the NAS until 1 a.m. and the editors start at 7 a.m. Run 1 at the full 1 Gbps says 4 hours, which looks easy. Run 2 turns the question around: to finish in those 6 hours, the copy has to hold 666.6667 Mbps the whole way. A test copy of one project opens near 110 MB/s in the copy dialog, then settles at a steady 85 MB/s, which is 680 Mbps once multiplied by 8. Run 3 at that sustained rate moves 1.836 TB in 6 hours, only 36 GB more than he needs, and solving for time at 680 Mbps gives 5h 52m 56s, about 7 minutes of slack. That is too thin to trust, so he skips the backup for one night and starts the copy at 11 p.m., which gives it 8 hours.
How much data a steady link moves in a minute, an hour, a day, and 30 days
Each cell is the data volume this calculator shows with Solve for set to Size, the link rate in the first column, and the time in the column header. The unit is the one picked in the data unit menu: MB for 1 minute, GB for 1 hour and 24 hours, and TB for 720 hours, which is 30 days because the time menu stops at hours. All units are decimal.
| Link rate | 1 minute | 1 hour | 24 hours | 720 hours (30 days) |
|---|---|---|---|---|
| 1 Mbps | 7.5 MB | 0.45 GB | 10.8 GB | 0.324 TB |
| 10 Mbps | 75 MB | 4.5 GB | 108 GB | 3.24 TB |
| 25 Mbps | 187.5 MB | 11.25 GB | 270 GB | 8.1 TB |
| 50 Mbps | 375 MB | 22.5 GB | 540 GB | 16.2 TB |
| 100 Mbps | 750 MB | 45 GB | 1080 GB | 32.4 TB |
| 300 Mbps | 2250 MB | 135 GB | 3240 GB | 97.2 TB |
| 500 Mbps | 3750 MB | 225 GB | 5400 GB | 162 TB |
| 1 Gbps | 7500 MB | 450 GB | 10800 GB | 324 TB |
| 2.5 Gbps | 18750 MB | 1125 GB | 27000 GB | 810 TB |
| 10 Gbps | 75000 MB | 4500 GB | 108000 GB | 3240 TB |
Computed with this tool's Size formula, bytes = bits per second x seconds / 8, then divided by the chosen unit and rounded to four decimals, which is why 1080 prints with no thousands separator and no trailing zeros. Pick GiB instead of GB and the 100 Mbps hour reads 41.9095 GiB, because 1 GiB is 1,073,741,824 bytes. Every cell is a ceiling. It assumes the full rate carries file data every second, with no packet overhead, no other traffic, and drives that keep up, so use these figures as upper bounds for a data cap check or an overnight sync.
What sets the real transfer rate
Size, speed, and time are one equation, size in bits = speed x time, and each Solve for mode rearranges it. Fix two and the third follows: double the speed and the time halves, double the time and twice the data fits. The catch is the speed. The equation assumes one steady rate, and a real copy runs at the rate of the slowest link in the chain, whether that is the source drive, the cable or network, the far server, or the destination drive. The units side of the problem, GB vs GiB and bits vs bytes, is covered in the download time calculator, so this section stays on where the rate comes from.
The number printed on a port is usually its signaling rate, not its data rate. SATA's 6 Gb/s link uses 8b/10b encoding, which puts 10 bits on the wire for every 8 bits of data, and SATA-IO rates the interface at 600 MB/s for that reason: 6 Gb/s x 8/10 = 4.8 Gb/s of data. The 5 Gbps USB rate, sold as USB 3.0 and now called USB 3.2 Gen 1, uses the same 8b/10b code, so at most 4 Gbps of it carries data before any protocol overhead. The 10 Gbps Gen 2 rate moved to 128b/132b encoding, which spends about 3 percent on the code instead of 20. Ethernet loses its share to packet headers and framing instead, and the download time calculator works that out.
Drives have a burst rate and a sustained rate. A hard drive spins at a constant speed and fits more sectors on its longer outer tracks, so it reads and writes faster near the edge of the platter than near the spindle. Rodney Van Meter measured this on multi-zone disks in a 1997 USENIX paper, and Seagate's hard drive data sheets quote a maximum sustained transfer rate at the outer diameter, marked OD, with a note that actual rates vary with the operating environment. So the same copy can run at different speeds depending on where on the platters the data sits. For a copy that has to fit a window, watch a real transfer for a few minutes after it settles and enter that rate, not the opening burst.
Network copies also start slowly. Under TCP congestion control (RFC 5681), a new connection begins with a small congestion window and grows it by at most one segment per acknowledgment, which roughly doubles it each round trip. RFC 6928, published as an experiment, raises the starting window to at most 10 segments and 14,600 bytes. In the ideal case, a connection on a 100 ms path needs about 7 round trips, 0.7 seconds, before it has the 1.25 MB in flight that a 100 Mbps line needs, so a file of a megabyte or so finishes before the connection reaches full speed. That is one reason thousands of small files copy far slower than one large file of the same total size, along with the work of creating each file at the destination. Time mode fits large single transfers best.
Size mode gives a ceiling, not a forecast. 100 Mbps held for 24 hours moves 1080 GB, and that is the most it could move, not what it will. The figure is still useful for ruling plans out. If the Size answer at your measured sustained rate is smaller than the data you have, no schedule will make the window work, and the options are a faster link, a longer window, or less data, such as copying only the files that changed since the last run.
Common mistakes
- Mixing decimal and binary size units without noticing. A file listed as 500 MiB by an operating system is not the same as 500 MB, and the gap widens as sizes grow into GB and TB territory.
- Assuming an ISP's advertised speed equals sustained real-world throughput. A '500 Mbps' plan rarely delivers a full, uninterrupted 500 Mbps to a single file transfer once overhead, Wi-Fi conditions, and server-side limits are factored in.
- Confusing bits and bytes when reading speed numbers. Network speeds are almost always quoted in bits per second (Mbps), while file sizes are quoted in bytes (MB), and treating the two as interchangeable produces an answer roughly 8 times off.
- Ignoring the slower end of the connection. A fast local network speed does not help if the file is being uploaded to or downloaded from a remote server with a much lower speed cap or heavy load.
- Forgetting that storage hardware has its own speed ceiling. A theoretically fast network or USB link is still limited by how quickly the source or destination drive can read or write data, especially for spinning hard drives or heavily fragmented storage.
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