How to use the Data Size Converter
- Enter a Size and pick a Unit. The table shows the value in bits, bytes, KB, MB, GB, TB and PB.
- Under Unit system, choose 1000 (how hard drive and USB drive makers label capacity) or 1024 (how Windows File Explorer shows sizes).
- In the Download and upload time calculator below, enter a file size and your internet speed to see how long the transfer should take in theory.
How many MB in a GB? 1000 vs. 1024
In the International System of Units (SI), kilo (K) means 1,000, so 1 GB = 1,000 MB. Computers work in binary, though, so multiples of 1,024 have also been common for a long time. To tell the two apart, binary units got their own names: KiB, MiB and GiB (kibibyte, mebibyte and gibibyte).
| Decimal (1000) | Value | Binary (1024) | Value |
|---|---|---|---|
| 1 KB | 1,000 B | 1 KiB | 1,024 B |
| 1 MB | 1,000,000 B | 1 MiB | 1,048,576 B |
| 1 GB | 10⁹ B | 1 GiB | 1,073,741,824 B |
| 1 TB | 10¹² B | 1 TiB | 1,099,511,627,776 B |
Base the unit system on where the number comes from. Drive packaging, phone storage specs and mobile data plans almost always use decimal units. Windows and some older software report sizes in binary units but still label them "KB", "MB" or "GB".
Why a 1TB drive shows up as 931GB
Storage makers label capacity in decimal units. Windows calculates in binary units and still calls the result "GB". A 1TB drive holds 10¹² bytes. Divided by 1,024³ (one GiB), that comes to about 931.3. None of the space is missing. The two numbers just use different units.
- 500GB → about 465.7GiB
- 1TB → about 931.3GiB
- 2TB → about 1,862.6GiB (about 1.82TiB)
Since Mac OS X 10.6 Snow Leopard (2009), macOS has shown sizes in decimal units, so the same drive appears as close to 1TB on a Mac.
Mbps vs. MB/s and how to calculate download time
A "100Mbps" internet plan means 100 megabits per second. One byte is 8 bits, so 100Mbps is about 12.5MB per second. Here's how to work out download time:
Time (seconds) = file size (bytes) × 8 ÷ speed (bits per second)
- 4GB movie at 100Mbps: 4,000,000,000 × 8 ÷ 100,000,000 = 320 seconds = 5 min 20 sec
- Same file on 1Gbps (gigabit) internet: 32 seconds
- 50GB game at 500Mbps: 13 min 20 sec
In practice, Wi-Fi conditions, server speed and protocol overhead often limit real speeds to about 60–90% of the theoretical figure. The calculator also shows how long the transfer would take at 80% of your connection speed.