Data Storage Units: KB, MB, GB, TB

Why does a brand new 500 GB hard drive show up as only about 465 GB in your file manager? Nothing is missing and nothing is broken. It comes down to how data storage units KB, MB, GB, and TB get counted, because there are two different ways to define the same unit name. Once you see the byte, kilobyte, megabyte, gigabyte, and terabyte ladder and the decimal versus binary split behind it, the “missing” space stops being a mystery.

What Are Data Storage Units?

Data storage units are the labels computers use to describe how much information a file, drive, or memory chip can hold. Every unit in the ladder is a multiple of the one below it, so the units scale up together in a predictable pattern.

The starting point is the byte. A single byte is made of 8 bits, and a bit is the smallest unit a computer stores. This article picks up from the byte and climbs upward. If you want the bit-level detail first, see our sibling guide, Bits vs Bytes Explained.

From the byte, the common storage ladder runs like this:

• Kilobyte (KB): about a thousand bytes
• Megabyte (MB): about a thousand kilobytes
• Gigabyte (GB): about a thousand megabytes
• Terabyte (TB): about a thousand gigabytes

Each step up is roughly 1,000 times bigger than the step before it, though the exact multiplier depends on whether you are counting in decimal or binary. That split is the key idea this article covers.

The Storage Unit Ladder From Byte to Terabyte

Picture the ladder as a staircase, where each step is a unit and every step up multiplies the size of the step before it. The chart below shows that climb from kilobyte up to terabyte.

In plain numbers, here is how the ladder works using decimal (1,000-based) counting, which is the system most storage manufacturers and marketing use:

• 1 KB = 1,000 bytes
• 1 MB = 1,000 KB = 1,000,000 bytes
• 1 GB = 1,000 MB = 1,000,000,000 bytes
• 1 TB = 1,000 GB = 1,000,000,000,000 bytes

That decimal pattern lines up with the metric system, where “kilo” means 1,000, “mega” means 1,000,000, and so on. The next section explains why some software counts these same unit names differently.

Decimal vs Binary: Two Ways to Count the Same Unit

Here is the part that trips people up. The names KB, MB, GB, and TB get used for two different counting systems, and both are common.

The decimal convention treats 1 KB as exactly 1,000 bytes, following the SI metric prefixes. This is the system storage manufacturers usually print on the box for hard drives, SSDs, and USB sticks, and it matches how the metric system counts everything else.

The binary convention instead treats “1 KB” as 1,024 bytes, because computers work in powers of two internally. Some operating systems display file and drive sizes this binary way, even while still labeling the unit “KB”, “MB”, or “GB” on screen.

To avoid the mix-up, there are separate binary unit names too: KiB, MiB, GiB, and TiB (kibibyte, mebibyte, gibibyte, tebibyte). These names are IEC standard terms built specifically for 1,024-based counting, so a KiB is always 1,024 bytes with no ambiguity.

Why Your Drive Shows Less Space Than Advertised

This is the real-world effect of the decimal versus binary split, and it is a well-known source of confusion. A manufacturer sells a “500 GB” hard drive using decimal counting, so the drive truly holds 500,000,000,000 bytes.

Your operating system, though, often reports drive size using binary counting while still calling the unit “GB”. To get that number, it divides the byte count by 1,073,741,824 (the number of bytes in 1 GiB), not by 1,000,000,000.

Do the math by hand: 500,000,000,000 divided by 1,073,741,824 equals about 465.7. That is why a “500 GB” drive shows up as roughly 465 GB (really 465 GiB) in the file manager. No storage vanished. The drive is being measured with a different ruler.

This gap grows as drives get bigger. A 1 TB drive (1,000,000,000,000 bytes) shows as about 931 GiB under binary counting, and a 4 TB drive shows as roughly 3.64 TiB. The larger the drive, the larger the visible gap looks, even though the percentage difference stays about the same, close to 7 percent.

Real-World Reference Sizes for Each Unit

Numbers like “1,048,576 bytes” are hard to picture. Real examples make the ladder easier to feel, even though actual file sizes vary a lot depending on format and quality.

Some typical, rounded examples to anchor the scale:

• Kilobytes (KB): a plain text document or a short email, often 10 to 100 KB
• Megabytes (MB): a single song file, commonly 3 to 8 MB
• Gigabytes (GB): a full length HD movie file, often 4 to 8 GB
• Terabytes (TB): a large external or internal hard drive, commonly 1 to 8 TB

These are typical ranges, not fixed rules. A photo, a phone app, or a video game can land at very different sizes depending on quality, compression, and length.

Quick Reference Table: Storage Units at a Glance

Use this table to check both counting systems side by side for the same unit name.

How to Convert Between Data Storage Units

Moving up the decimal ladder, you divide by 1,000 to go down a step, and multiply by 1,000 to go up a step. For example, 2,500 MB divided by 1,000 equals 2.5 GB. Going the other way, 2.5 GB times 1,000 equals 2,500 MB.

The binary ladder works the same way, just with 1,024 instead of 1,000. So 2,048 MiB divided by 1,024 equals 2 GiB.

Doing this by hand across several units at once gets tedious and easy to mess up, especially when you need to switch between decimal and binary counting. Our Data Storage Converter handles both systems for you, so you can move between KB, MB, GB, TB, and their binary counterparts in one step.

Two related topics sit next to this one but are not covered here. If you want the bit-level basics behind the byte, see Bits vs Bytes Explained. If you want to know how long a file of a given size takes to download, see How to Estimate File Download Time, which also covers bandwidth in Mbps.

Frequently Asked Questions About Data Storage Units

Sources

This article is for general education only. Real-world file sizes, speeds, and network conditions vary, so actual results can differ from the examples shown. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 13, 2026.