Free Data Size Converter (Bytes, KB, MB, GB, TB)
Free data size converter. Enter a byte count to convert it into all common units — KB, MB, GB, TB, and more — at once. Shows both the decimal (SI, base-1000) and binary (IEC, base-1024) systems side by side, and explains why file size displays don't always match across apps.
Decimal (SI)
Binary (IEC)
Why "file size" displays don't match across apps
Units like KB, MB, and GB actually come in two systems: "decimal (SI)," which advances by 1000, and "binary (IEC)," which advances by 1024. The same byte count produces different displayed numbers depending on which system is used, which is exactly why "the file size shown doesn't match" confusion happens between different OSes and apps.
| Unit | Bytes in decimal (SI) | Bytes in binary (IEC) |
|---|---|---|
| KB / KiB | 1,000 B | 1,024 B |
| MB / MiB | 1,000,000 B | 1,048,576 B |
| GB / GiB | 1,000,000,000 B | 1,073,741,824 B |
| TB / TiB | 1,000,000,000,000 B | 1,099,511,627,776 B |
What is a data size converter?
A data size converter lets you enter a byte count and instantly get it translated into the everyday units you actually deal with — KB, MB, GB, TB, and beyond. Whenever you're working with file sizes, storage capacity, or data transfer volumes, it saves you from redoing the same digit-shifting math by hand or in a plain calculator.
What sets this tool apart is that it shows decimal (SI, base-1000) and binary (IEC, base-1024) results side by side at the same time. Because the same byte count produces a different number depending on which system is used, looking at only one system can leave you puzzled by why file sizes seem to disagree between different apps.
How to use it
- Enter the number you want to convert Type in whatever value you already have on hand — a byte count, a KB figure, a GB figure, and so on.
- Choose the unit of your input Pick the unit that matches the number you just entered, from bytes all the way up to KiB and beyond, from the dropdown.
- Check the decimal and binary tables Your input is automatically converted into every unit under both the SI (decimal) and IEC (binary) systems, laid out as tables.
- Read off the value for the unit you need Find the row for the unit you're after — say, MB or GiB — in the tables and read the converted figure.
Tips for getting more out of it
- macOS Finder uses decimal (SI) notation, while Windows Explorer keeps labels like GB and MB but actually calculates in binary (IEC) under the hood — so the same file can show a different size number depending on the OS.
- Hard drive and SSD manufacturers commonly use decimal (SI) notation for advertised capacity, which is why a drive can appear to have "less capacity than advertised" once your OS reports it — that's not actually missing storage, just a difference in how the units are calculated.
- Network speeds (bps) are generally calculated in decimal (1 Mbps = 1,000,000 bps), so naively estimating download time as "file size (often IEC) ÷ line speed (SI)" introduces some error worth keeping in mind.
- You can select a unit and enter a value in the input field, so this also works directly for converting between units — e.g. "how many MiB is 5 GB?" or "how many MB is 500 MiB?"
Use cases
Working out free space in cloud storage
Subtract byte-level usage from your plan's total capacity and read the remaining space back in an easy-to-grasp GB or TB figure.
Estimating video and photo file sizes
Convert the combined byte count of your footage into GB or TB to check ahead of time whether it will fit on an SD card or external drive.
Sizing server and database storage
Multiply your expected record count by the bytes per record, then convert the resulting total into whatever unit your disk plan is quoted in for an easy comparison.
Tracking API or network data caps
Convert the total bytes used by API responses or monthly data transfer into the GB figure your plan advertises, so you can see how close you are to the limit.
Glossary
- SI prefix
- A prefix defined by the International System of Units (SI) that scales by 1000 at each step — k (kilo), M (mega), G (giga), and so on — used for the decimal notation of data sizes.
- IEC prefix
- A prefix defined by the International Electrotechnical Commission (IEC) in 1998 that scales by 1024 at each step — Ki (kibi), Mi (mebi), Gi (gibi), and so on — used to make binary notation explicit.
- Octet
- A term for a group of 8 bits, used almost interchangeably with "byte." Networking specifications tend to use the stricter term "octet" instead.
- Petabyte
- A unit equal to another 1000x (decimal) or 1024x (binary) beyond terabyte, commonly used to describe the total capacity of large data centers or an entire cloud service.
Frequently Asked Questions
Side Note — why "KiB" was born in 1998
The convention of "1 KB = 1024 bytes" took hold in computing because 2 to the 10th power (1024) was a natural, round number for machines built on binary. But under the International System of Units (SI), the prefix "kilo" strictly means a factor of 1000, so this convention was at odds with the actual definition of the SI prefix all along.
This contradiction became especially visible around hard drive capacity labeling. Drive manufacturers strictly followed SI, advertising "1 GB" as one billion bytes, while operating systems calculated 1 GB as roughly 1.074 billion bytes (1024 cubed) — leading to a steady stream of consumer complaints that a purchased drive showed "less capacity than advertised" once viewed in the OS. In reality, no capacity was actually missing; it was purely a difference in calculation method.
To resolve this confusion, the International Electrotechnical Commission (IEC) defined new prefixes dedicated to binary (base-1024) counting in 1998 — Kibi (Ki), Mebi (Mi), Gibi (Gi), and so on. In theory, this cleanly separated the roles: "KB" strictly follows SI's base-1000, while "KiB" denotes binary's base-1024. In practice, though, the habit of using "KB" to mean base-1024 remains deeply entrenched among everyday users to this day.