Why Your "1TB" Laptop Shows Only 931GB: MiB vs MB Explained
Decimal Byte vs Binary Byte (iB Units)
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Have you ever bought a 1TB laptop or external hard drive, only to find that your operating system shows something like 931GB instead?
Don’t worry, your storage isn’t broken. Manufacturer is also not scamming you by false advertisement. This happens because of the way computers and manufacturers measure data. Lets try to understand it with following examples :
Marketing vs Reality
When manufacturers advertise 1TB (terabyte) of storage, they usually mean:
- 1TB = 1,000,000,000,000 bytes (decimal system, base 10)
But your operating system (Windows, Linux, macOS) doesn’t read it the same way. Computers work in binary (base 2). So instead of grouping bytes by powers of 10, they group them by powers of 2.
That’s where MiB (Mebibyte) vs MB (Megabyte) comes in.
MB vs MiB, GB vs GiB, TB vs TiB
| Unit (SI / Marketing) | Based on Decimal (10) | Unit (Binary / OS) | Based on Binary (2) |
| 1 KB = 1,000 bytes | 10³ | 1 KiB = 1,024 bytes | 2¹⁰ |
| 1 MB = 1,000,000 bytes | 10⁶ | 1 MiB = 1,048,576 bytes | 2²⁰ |
| 1 GB = 1,000,000,000 bytes | 10⁹ | 1 GiB = 1,073,741,824 bytes | 2³⁰ |
| 1 TB = 1,000,000,000,000 bytes | 10¹² | 1 TiB = 1,099,511,627,776 bytes | 2⁴⁰ |
Notice that 1 TB (decimal) is smaller than 1 TiB (binary).
The "1TB = 931GB" explained
When you buy a 1TB drive, manufacturers mean:
1TB = 1,000,000,000,000 bytes
But your OS measures it in GiB (binary GB):
1 GiB = 1,073,741,824 bytes
So, your 1TB drive is actually:
1,000,000,000,000 ÷ 1,073,741,824 ≈ 931 GiB
That’s why your 1TB laptop shows ~931GB. (which is actually 931 GiB)
Some more Examples
500GB HDD → ~465GB in your system
256GB SSD → ~238GB usable
128GB USB Drive → ~119GB
1TB Laptop → ~931GB
Why Does This Happen?
Manufacturers use decimal (SI units) for marketing → larger numbers look better.
Operating systems use binary units (IEC standard) → true computer representation.
Result : Confusion for users who think they’re losing storage.
Formatting Overhead
Even after the conversion difference, you may notice slightly less space. That’s because storage devices need to reserve a small portion for:
File system metadata (NTFS, ext4, APFS, etc.)
Partition tables
System-reserved space
So your available storage is always a little less than what’s advertised.
Next time you buy a storage device, you’ll know why storage space doesn’t match the box.
