Data Storage Unit Converter
Convert between bytes, KB, MB, GB, TB, and PB, with a toggle for decimal vs binary calculation.
How to use this tool
Type a number into any field and the rest recalculate immediately. Use Decimal (1000-based) to match manufacturer packaging, or Binary (1024-based) to match what your OS reports as free space.
Why decimal and binary give different answers
"Kilo," "mega," and "giga" have two competing definitions in computing. The strict SI (decimal) definition treats kilo as exactly 1,000, mega as 1,000², and so on — what storage manufacturers use when advertising capacity on packaging. The binary definition instead uses powers of 1,024 (2¹⁰), which is how memory has traditionally been addressed and is what most operating systems use when reporting free space. Neither is wrong; they're just answering "how big is a kilobyte" differently.
Worked example
A drive advertised as exactly 1 TB (decimal) holds 1,000,000,000,000 bytes. Plug that same byte count into the Binary (1024-based) toggle and it converts to only about 931 GB — not because any storage went missing, but because the OS is dividing by 1,024⁴ instead of 1,000⁴ to compute gigabytes. This exact mismatch is why a new drive's properties dialog always shows less space than the number on the box.
Frequently Asked Questions
Why do manufacturers and operating systems disagree on drive capacity?
Drive makers use the SI meaning of kilo, mega, giga and tera, so a 1 TB drive holds 10¹² bytes. Windows divides by 1024 at each step but still writes GB, which turns those 10¹² bytes into 931 GB. macOS has counted in 1000s since Snow Leopard in 2009 (Apple's support page says OS X Leopard and earlier used binary), so a Mac shows the same drive as 1 TB. Neither is a miscount; they read the same unit names differently.
What is the difference between KB and KiB?
KiB (kibibyte) unambiguously means 1024 bytes — a binary unit created specifically to end the KB ambiguity. KB (kilobyte) technically means 1000 bytes under SI standards, but is very commonly used loosely to mean 1024 bytes in casual and OS contexts, which is exactly the ambiguity that causes confusion. This tool's Decimal/Binary toggle lets you compute either definition explicitly rather than guessing which one applies.
Can I use this for internet speeds like 100 Mbps?
Only after one extra step. Connection speeds are quoted in bits per second, and this converter works in bytes, which are 8 bits each. Divide by 8 first: 100 Mbps is 12.5 megabytes a second (decimal), so a 1 GB download takes at least 80 seconds on that line, before any overhead.
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