File Size Calculator - Convert KB, MB, GB, TB & GiB

About the File Size Calculator

Digital sizes cause a surprising amount of confusion. A new 1 TB drive shows up as 931 GB on a computer, a phone says a video is 1.5 GB while a laptop says 1.4, and internet speeds are quoted in megabits while downloads are measured in megabytes. None of this means anything is wrong: there are two ways of counting bytes, decimal and binary, and bits and bytes are different units.

This file size calculator converts any size between bytes, decimal units (KB, MB, GB, TB), binary units (KiB, MiB, GiB, TiB) and bits. It shows the size in every unit at once, and explains how the same size will be shown by a drive label and by a computer that counts in 1,024s.

How to Use the File Size Calculator

Enter the size as a number.

Choose its unit: decimal units such as MB and GB, binary units such as MiB and GiB, or bit units such as Mb (megabits) and Gb (gigabits), which are used for network speeds and some memory chips.

The calculator converts it to bytes and then to every other unit.

Decimal and Binary Units

  Decimal (SI)                 Binary (IEC)
  1 KB = 1,000 bytes           1 KiB = 1,024 bytes
  1 MB = 1,000 KB              1 MiB = 1,024 KiB = 1,048,576 bytes
  1 GB = 1,000 MB              1 GiB = 1,024 MiB = 1,073,741,824 bytes
  1 TB = 1,000 GB              1 TiB = 1,024 GiB

  1 byte = 8 bits

Decimal units follow the metric system, where kilo means a thousand. Drive makers, phone makers and network providers use them. Binary units step by 1,024, a power of two that suits computer memory, and have their own names — kibibyte, mebibyte, gibibyte — to avoid confusion. Some operating systems count in binary but still label the result KB, MB and GB, which is where most of the confusion comes from.

Step-by-Step Example

How big is a 1 TB drive?

  Bytes:     1 TB = 1,000,000,000,000 bytes
  KiB:       10¹² ÷ 1,024 = 976,562,500 KiB
  MiB:       ÷ 1,024 again = 953,674 MiB
  GiB:       ÷ 1,024 again = 931.323 GiB
  TiB:       ÷ 1,024 again = 0.909495 TiB

So the drive holds 1,000,000,000,000 bytes, exactly as labelled, but a computer counting in 1,024s shows it as about 931 GiB — often written as "931 GB". Nothing is missing; the units are different.

A 1.5 GB file is 1,500,000,000 bytes: 1,500 MB in decimal units, or about 1,430.51 MiB and 1.39698 GiB in binary units. A phone showing decimal units calls it 1.5 GB, while a computer showing binary units might call it 1.4 GB.

Why the Gap Grows

Each step up in binary units multiplies by 1,024 instead of 1,000, so the difference compounds. A kibibyte is 2.4 percent larger than a kilobyte, a gibibyte about 7.4 percent larger than a gigabyte, and a tebibyte almost 10 percent larger than a terabyte. That is why the gap between the label and what a computer shows looks small on a USB stick but large on a big hard drive.

Drives also lose a little space to formatting and the file system, and computers may reserve space for recovery partitions, so the free space shown is usually a little less again.

Bits and Bytes

A byte is 8 bits. File sizes are measured in bytes, with a capital B, while network speeds are measured in bits per second, with a small b. A 100 megabit (100 Mb) amount of data is 12.5 megabytes, and a 1 MB file is 8 megabits. Mixing them up makes downloads look eight times slower than expected.

Sizes in Everyday Terms

A terabyte is about 1,000 GB: roughly 250,000 phone photos of 4 MB each, 500 hours of HD video at 2 GB an hour, or around 200,000 songs at 5 MB each. Real numbers vary with the quality setting, the format and how busy the scene is, since compressed files depend on their content as well as their length.

Memory, Cards and Cloud Storage

Computer memory, RAM, is built in powers of two, so a 16 GB memory module really holds 16 GiB, 17,179,869,184 bytes. Memory cards and USB sticks follow drive makers and use decimal units, so a 128 GB card holds about 119 GiB. Cloud storage plans vary: some count in decimal units and some in binary, and their help pages usually say which. When a plan gives a quota in GiB or TiB, convert your files to the same unit before judging how much will fit.

Reading Sizes in Software

Different programs choose different conventions. Many phones and some desktop systems now show decimal units, matching the labels on drives, while others still show binary values with decimal names. Command-line tools often let you choose, and some print KiB, MiB and GiB explicitly. If two programs disagree about the size of the same file by about 5 to 10 percent, the difference is almost certainly decimal versus binary counting rather than a problem with the file.

Understanding Your Result

The headline gives the size in bytes, the basic unit everything else is built on.

The decimal line gives the size in KB, MB, GB and TB.

The binary line gives the size in KiB, MiB, GiB and TiB.

The bits line gives the size in bits and megabits, for comparing with network speeds.

The shown line explains how a drive label and a binary-counting computer will describe the same size.

When Should You Use This Calculator?

Use it when a drive, card or phone shows less space than the label promised.

Use it to convert file sizes between the units used by different devices and programs.

Use it when working with memory, storage or cloud limits given in GiB or TiB.

Use it to compare file sizes with network speeds in bits.

Common Mistakes

Thinking storage is missing. The difference between a label and the space shown is usually just decimal versus binary units.

Confusing bits and bytes. Mb is megabits, MB is megabytes, eight times larger.

Assuming GB always means the same. Check whether a program counts in 1,000s or 1,024s.

Adding up without converting. Mixing decimal and binary figures in one total gives a wrong answer.

Forgetting file system space. A formatted drive has slightly less usable space than its raw size.