File Size Calculator

Converting File Sizes Without Losing Track of the Base

A photo listed as "4.2 MB," a game update listed in GB, and a cloud storage quota listed in TB all use the same unit names but not always the same underlying byte count. This calculator moves a value between bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes under whichever convention you specify — the binary base used by most operating systems, or the decimal base used by storage manufacturers and cloud providers.

The Formula

Every conversion passes through bytes as the common intermediate unit:

Bytes = Value × (Size of source unit in bytes)
Result = Bytes / (Size of target unit in bytes)

Under the binary convention, each step up is ×1024 (1 KB = 1024 B); under the decimal convention, each step is ×1000 (1 KB = 1000 B) — the same structure as the formal IEC vs. SI distinction, applied consistently through KB, MB, GB, TB, and PB.

Where This Calculation Matters

Comparing quoted file sizes — converting a size quoted in one unit into the unit you actually need to compare against a limit or quota.
Explaining a size discrepancy — a value that looks "wrong" between two systems is often just the same byte count expressed under different base conventions, not an actual data mismatch.
Media production specs — converting between the decimal GB used in disc capacity specs (a standard DVD is quoted as 4.7 GB, decimal) and the binary units a video editor might report.
Cloud storage tiers — checking exactly how many MB or GB a storage plan's listed capacity represents before estimating how many files it will hold.

Same Value, Two Conventions

Worked conversions showing the binary vs. decimal difference
Conversion	Binary (1024-based)	Decimal (1000-based)
750 MB → GB	0.7324 GB	0.75 GB
1 GB → MB	1,024 MB	1,000 MB
4.7 GB (DVD spec) → MB	4,812.8 MB	4,700 MB

A single-layer DVD is specified as 4.7 GB using the decimal convention — converted with the binary convention instead, it works out to roughly 4.38 "GiB," which is why some software reports its capacity differently.

How to Use This Calculator

Enter the Value you want to convert.
Choose the From unit and To unit, from B up through PB.
Select the Binary (1 KB = 1024 B) or Decimal (1 KB = 1000 B) base.
Select Calculate to get the converted value.

Related Calculations

Need bit-level units like bits and Kbps included in the conversion? Use the Storage Calculator. Estimating a video or audio file's size from its bitrate instead? See the Video Bitrate Calculator.