Why 1 TB shows up as 931 GB
There are two competing systems for naming data sizes. Storage manufacturers, network engineers and the SI standard use decimal prefixes: 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 10^9 bytes, 1 TB = 10^12 bytes. Operating systems and memory makers grew up on powers of two: 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 2^30 bytes, 1 TiB = 2^40 bytes. Windows uses the binary values but labels them KB, MB, GB and TB, which is where the confusion comes from.
The gap is 2.4% per step and compounds: a 1 TB drive holds 1,000,000,000,000 bytes, and 10^12 / 1024^4 = 931.32, so Windows reports 931 GB. A 500 GB SSD reports 465 GB, a 2 TB drive reports 1.82 TB, and a 128 GB phone reports about 119 GB before the operating system takes its share. macOS switched to decimal in 2009, which is why the same drive shows 1 TB on a Mac and 931 GB on a PC. RAM is always binary: 16 GB of memory is really 16 GiB.
Bits, bytes and download time
A byte is 8 bits. Storage is quoted in bytes (capital B), while internet plans are sold in megabits per second (Mbps, lowercase b). To turn Mbps into MB/s, divide by 8: a 100 Mbps plan moves at most 12.5 MB/s, so a 1 GB file (10^9 bytes) takes about 80 seconds, and a 50 GB game download takes roughly 67 minutes. A gigabit connection (1,000 Mbps) tops out at 125 MB/s.
Real downloads rarely hit the advertised speed because of Wi-Fi, server limits and protocol overhead; planning on 70 to 90 percent of the rated speed is realistic. Enter your plan speed in the form and the converter shows a theoretical time for the size you entered. Mobile plans and cloud storage tiers usually bill in decimal GB, while phone settings screens show binary values, so a 5 GB data cap is about 4.66 GiB as your phone counts it.
How to use the converter
Enter a number, pick its unit, and tell the converter which system the number came from. A drive box, a cloud plan or an ISP page is decimal; a Windows properties dialog or a RAM spec is binary. The output table lists both systems for every unit so you can see, for example, that 4.7 GB on a DVD label is 4.38 GiB, or that a 25 GiB Blu-ray is 26.8 GB. The IEC names KiB, MiB, GiB and TiB (kibibyte, mebibyte, gibibyte, tebibyte) exist precisely to remove the ambiguity, even though most people still say gigabyte for both.