Computer Storage Units: Bit, Byte, KB, MB, GB, TB, PB and How to Convert

Hello my friend! 💾 You buy 1 TB hard disk, but Windows show only 931 GB. Where the rest go? 🤔 Today we learn computer storage unit — bit, byte, KB, MB, GB, TB, PB and more — and how to convert from one unit to other. Very useful for every computer user!

1. Smallest Unit: Bit and Byte

Computer only understand 0 and 1. Everything — photo, video, game, document — is keep as many 0 and 1.

• Bit (b): Smallest unit. One bit = one 0 or one 1.
• Nibble: 4 bit. (Not use much, but good to know.)
• Byte (B): 8 bit. One byte can keep one letter, like A or z.

1 Byte = 8 bits
Letter "A" = 01000001  ← 8 bit = 1 byte

Remember: small b = bit, big B = Byte. Very important! 100 Mb and 100 MB is not same.

2. Storage Unit Table (Small to Big)

Each step bigger is about 1,000 times (or exactly 1,024 — see section 3).

Unit	Short	Size (decimal)	Real-life example
Bit	b	0 or 1	One switch on/off
Byte	B	8 bit	One letter
Kilobyte	KB	1,000 Byte	Short text file
Megabyte	MB	1,000 KB	One photo from phone (2–5 MB)
Gigabyte	GB	1,000 MB	One HD movie (1–4 GB), RAM size
Terabyte	TB	1,000 GB	External hard disk, big SSD
Petabyte	PB	1,000 TB	Data center, big company storage
Exabyte	EB	1,000 PB	Big cloud like Google, Microsoft
Zettabyte	ZB	1,000 EB	All data in the world in one year
Yottabyte	YB	1,000 ZB	Too big, no device have this yet
Ronnabyte	RB	1,000 YB	New unit (added in 2022)
Quettabyte	QB	1,000 RB	New unit (added in 2022), biggest now

Easy way to remember order: K → M → G → T → P → E → Z → Y

3. 1,000 or 1,024? Decimal vs Binary

This part make many people confuse. There are 2 system:

• Decimal (base 10): 1 KB = 1,000 Byte. Hard disk and USB maker use this. Also internet speed.
• Binary (base 2): 1 KiB = 1,024 Byte. Computer work in power of 2, so Windows and RAM use this.

Binary unit have special name with "i" in middle: KiB (kibibyte), MiB (mebibyte), GiB (gibibyte), TiB (tebibyte), PiB (pebibyte).

Decimal	Byte	Binary	Byte	Different
1 KB	1,000	1 KiB	1,024	2.4%
1 MB	1,000,000	1 MiB	1,048,576	4.9%
1 GB	1,000,000,000	1 GiB	1,073,741,824	7.4%
1 TB	1,000,000,000,000	1 TiB	1,099,511,627,776	10.0%
1 PB	1015	1 PiB	250 = 1,125,899,906,842,624	12.6%

See? Bigger unit = bigger different.

Why 1 TB Hard Disk Show Only 931 GB?

Hard disk maker count: 1 TB = 1,000,000,000,000 Byte (decimal).

Windows count with 1,024, but still write "GB" (really mean GiB):

1,000,000,000,000 ÷ 1,024 ÷ 1,024 ÷ 1,024 = 931.32 GB

So no space is missing! Just 2 different way to count. Same thing happen with other size:

You buy	Windows show
128 GB	119.2 GB
256 GB	238.4 GB
500 GB	465.7 GB
1 TB	931.3 GB
2 TB	1.81 TB

(Real number a bit less again, because some space use for format and system file.)

4. How to Convert — Easy Method

Only remember 2 rule:

• ⬆️ Small unit → Big unit: Divide (÷ 1,000 or ÷ 1,024)
• ⬇️ Big unit → Small unit: Multiply (× 1,000 or × 1,024)

Each step you move, divide or multiply one time.

        × 1,000      × 1,000      × 1,000      × 1,000
   TB  ─────────▶ GB ─────────▶ MB ─────────▶ KB ─────────▶ Byte
   TB  ◀───────── GB ◀───────── MB ◀───────── KB ◀───────── Byte
        ÷ 1,000      ÷ 1,000      ÷ 1,000      ÷ 1,000

Example 1: GB → MB (big to small, multiply)

2.5 GB = 2.5 × 1,000 = 2,500 MB     (decimal)
2.5 GB = 2.5 × 1,024 = 2,560 MB     (binary)

Example 2: MB → GB (small to big, divide)

3,072 MB = 3,072 ÷ 1,024 = 3 GB     (binary)

Example 3: Jump many step — TB → MB

From TB to MB is 2 step (TB → GB → MB), so multiply 2 time:

2 TB = 2 × 1,000 × 1,000 = 2,000,000 MB

Example 4: Byte → GB

From Byte to GB is 3 step, so divide 3 time:

5,000,000,000 Byte = 5,000,000,000 ÷ 1,000 ÷ 1,000 ÷ 1,000 = 5 GB

Example 5: How many photo can keep in 64 GB?

64 GB = 64 × 1,000 = 64,000 MB
One photo = 4 MB
64,000 ÷ 4 = 16,000 photo  (about)

Quick Conversion Table (Decimal)

From → To	Do this
KB → MB	÷ 1,000
MB → GB	÷ 1,000
GB → TB	÷ 1,000
TB → PB	÷ 1,000
GB → MB	× 1,000
TB → GB	× 1,000
TB → MB	× 1,000,000
PB → GB	× 1,000,000
Byte → bit	× 8
bit → Byte	÷ 8

For binary (Windows, RAM), just change 1,000 to 1,024.

5. Bonus: Internet Speed (Mbps vs MB/s)

Internet speed use bit (small b), not Byte:

• Mbps = Megabit per second (internet package, Wi-Fi speed)
• MB/s = Megabyte per second (download speed in browser)

Because 1 Byte = 8 bit, just divide by 8:

100 Mbps ÷ 8 = 12.5 MB/s

How long to download 5 GB game with 100 Mbps internet?

5 GB = 5,000 MB
5,000 MB ÷ 12.5 MB/s = 400 second ≈ 6 minute 40 second

(Real life a bit slower, because network not always full speed.)

Want learn more about Mbps, Gbps, and download time? Read Internet Bandwidth Units and How to Convert.

Internet package	Max download speed
20 Mbps	2.5 MB/s
50 Mbps	6.25 MB/s
100 Mbps	12.5 MB/s
1 Gbps (1,000 Mbps)	125 MB/s

Tips

• Small b = bit, big B = Byte. Always check letter when read internet package or download speed.
• Divide when go up (small → big), multiply when go down (big → small). Only this 2 rule!
• Hard disk, USB, and internet use 1,000. Windows and RAM use 1,024. That's why number not match.
• Buy storage bigger than you need. Windows, update, and app take more space every year.
• Keep at least 10–15% free space on your system drive (C:). Full drive make computer slow.
• Quick estimate: 1 GB ≈ 250 song, ≈ 250 photo, or ≈ 20–30 minute Full HD video. Good for plan space.
• Use Google search for fast convert: type 2.5 GB to MB and Google answer for you.

Conclusion

Now you understand computer storage unit from bit until petabyte and more. Remember: 8 bit = 1 Byte, each unit is 1,000 (or 1,024) times bigger, divide to go up, multiply to go down. And now you know why 1 TB disk show 931 GB — nothing missing! Keep learning my friend! 💡

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