Convert decimal and binary storage units plus bits and bytes — and finally see why a 1 TB drive shows up as 931 GB.
There are two incompatible ways to count storage and both are in daily use, which is where nearly all confusion about disk sizes comes from. The decimal units follow the SI prefixes literally: 1 KB is 1,000 bytes, 1 MB is 1,000 KB, 1 GB is 1,000 MB. The binary units, standardized as KiB, MiB, GiB and TiB, step by 1,024 instead, because 1,024 is 2¹⁰ and memory addressing is binary. This converter puts both families in the same table, with bits alongside them, and converts everything through the bit as a pivot so no rounding creeps in.
That difference is exactly why a drive sold as "1 TB" appears as 931 GB in Windows. The manufacturer is telling the truth in decimal units — the disk really holds 1,000,000,000,000 bytes — but Windows divides by 1,024 four times and displays the result as "TB" when it is actually TiB, arriving at 0.909 TiB, or 931 GiB. Nothing is missing and nobody is cheating: the same disk is being described in two different unit systems that share a label. The gap widens as the numbers grow, from about 2.4% at the kilobyte level to 9.1% at the terabyte level. macOS and most Linux file managers report decimal GB, which is why the same drive looks bigger there than on Windows.
The second trap is bits versus bytes. A byte is 8 bits, and the two are written with the same letters in different cases: Mb (megabit) and MB (megabyte), Mbps and MB/s. Internet plans are always sold in bits per second, while download managers and file sizes are shown in bytes, so a 300 Mbps fibre plan tops out at 37.5 MB/s and a 100 Mbps link at 12.5 MB/s — divide by 8. Use this converter to size a backup against a disk, to check whether a video fits an upload limit, to translate a RAM figure between GB and GiB, or simply to settle the argument about the missing gigabytes. It runs 100% in your browser, with nothing uploaded.
Everything is converted through the bit: 1 byte = 8 bits. Decimal: 1 KB = 1,000 B · 1 MB = 1,000 KB · 1 GB = 10⁹ B · 1 TB = 10¹² B · 1 PB = 10¹⁵ B. Binary: 1 KiB = 1,024 B · 1 MiB = 1,024 KiB · 1 GiB = 2³⁰ B = 1,073,741,824 B · 1 TiB = 2⁴⁰ B. Therefore 1 GB = 0.93132257 GiB, 1 TB = 0.9094947 TiB and 100 Mb = 12.5 MB.
Because the two numbers use different units with the same label. The manufacturer counts 1,000,000,000,000 decimal bytes; Windows divides that by 1,024 three times and shows 931 — which is really 931 GiB, not GB. No space is lost, and formatting overhead accounts for only a small extra fraction.
A GB (gigabyte) is 1,000,000,000 bytes and a GiB (gibibyte) is 1,073,741,824 bytes — 2³⁰. GiB is 7.4% larger, so 1 GB equals about 0.9313 GiB.
12.5 MB/s at most. Divide the megabits by 8 to get megabytes, since one byte is eight bits. Real-world speeds are a little lower because of protocol overhead.
Use binary units (KiB, MiB, GiB) for RAM, block sizes, memory addressing and anything an operating system reports internally. Use decimal units (KB, MB, GB) for disk and SSD capacities, network rates and bandwidth caps, which are defined that way by the industry.
No. The whole conversion is a few multiplications done in JavaScript on your device — nothing is uploaded, transmitted or stored.
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