File and Disk Size Converter

Size:

Enter one file, folder, volume, quota, or device size and keep its unit explicit.

Convert to:

Choose the notation needed for a report, purchase comparison, quota, or migration plan.

Plain-label basis:

Use Decimal unless the source explicitly uses plain labels for binary values.

Sizing goal:

Choose the decision the headline should answer; every artifact remains byte-anchored.

Reserve and metadata:

Zero is neutral. Use a measured or policy-approved percentage when available.

Allocation unit:

No rounding is neutral. Choose a cluster or extent size only for an allocation-aware estimate.

Estimated file count:

One is neutral. A representative file count makes small-file slack visible.

files

Display precision:

Use more decimals when reconciling large SI and IEC labels.

Unit	Equivalent value	Basis	Copy
{{ row.label }}	{{ row.value }}	{{ row.basis }}

Decision	Current reading	Next check	Copy
{{ row.label }}	{{ row.reading }}	{{ row.action }}

A storage label is useful only when its byte basis is clear. Drive vendors, media capacities, and many quotas use decimal prefixes, while technical tools may report the same bytes with binary IEC prefixes. One trillion bytes is exactly 1 TB in decimal notation but about 931.323 GiB in binary notation.

Storage quantities that should not be confused
Quantity	Meaning	Typical cause of disagreement
Payload bytes	Logical size of the files or data	Compression, sparse files, and hidden data
Raw capacity	Bytes named by a device, volume, or tier	Decimal versus binary labels
Usable capacity	Raw capacity after a planning reserve	Metadata, snapshots, policy headroom, and working space
Allocated size	Payload rounded to storage allocation units	Many small files occupying whole clusters or extents

Explicit IEC labels such as KiB, MiB, GiB, and TiB always use powers of 1024. Plain KB, MB, GB, and TB usually use powers of 1000, but older software sometimes applies binary math while displaying a plain label. That legacy shorthand must be identified before converting.

A capacity plan also needs workload shape. A handful of large backup images may waste little allocation space, whereas millions of small files can round up substantially. Reserve and allocation slack describe different effects and should not be combined into one unexplained percentage.

The result is a planning model, not a scan of a real disk. File-system metadata, snapshots, deduplication, compression, sparse allocation, deleted-but-open files, controller behavior, and storage faults can change observed available space. Verify the target system before a purchase, migration, or cleanup decision.

How to Use This Tool:

Start with the label you have, define its byte basis, and add reserve or allocation assumptions only when capacity planning needs them.

Enter Size, its source unit, and the unit needed for the converted result.
Choose the Plain-label basis. Use decimal for vendor and network-style labels; choose legacy binary only when the source clearly used 1024-step math with KB, MB, GB, or TB.
Set Sizing goal to pure conversion, raw-capacity analysis, or payload-to-store planning.
Enter a measured or approved Reserve and metadata percentage from 0% to 30%. Choose an Allocation unit and representative file count only when estimating slack.
Check Capacity fit for the first built-in tier that holds the modeled allocated bytes after reserve. Increase precision when reconciling large SI and IEC values.

Interpreting Results:

Converted value is a unit change anchored to the same byte count. A smaller-looking GiB or TiB number does not by itself indicate missing capacity.

Allocated bytes adds modeled rounding slack. Required raw bytes then expands that allocation so the payload still fits after the selected reserve is removed. The first-fit tier uses the same reserve and allocation assumptions.

A fit result can be overconfident when average file size is not representative. Compare the model with a real file-count and size-on-disk report before selecting hardware or setting a quota.

Technical Details:

Bytes are the shared unit for every conversion. Decimal plain labels use factors of 1000; IEC labels use factors of 1024. Legacy binary mode changes only plain KB through EB labels, while explicit KiB through EiB remain binary.

Formula Core:

Let x be the entered size, f_from and f_to the source and destination unit factors, n the file count, a the allocation unit in bytes, and r the reserve fraction.

\begin{array}{lcl} B & = & x \times f_{from} \\ x_{converted} & = & \frac{B}{f_{to}} \\ B_{allocated} & = & n \times a \times ⌈ \frac{B}{n a} ⌉ \\ B_{required raw} & = & \frac{B_{allocated}}{1 - r} \end{array}

When no allocation rounding is selected, allocated bytes equal payload bytes. Otherwise the model divides payload bytes evenly across the estimated files, rounds that average file size up to a whole allocation unit, and multiplies by the file count. Slack equals allocated bytes minus payload bytes.

Usable capacity for an entered raw size is B × (1 − r). Each built-in storage tier is tested in the same way, and the first tier whose usable bytes are greater than or equal to allocated bytes is the first fit. A zero-byte payload has no fit tier.

Unit Core:

Decimal and IEC storage unit factors
Family	Examples	Factor per step
Decimal	KB, MB, GB, TB	1000
IEC binary	KiB, MiB, GiB, TiB	1024
Legacy binary plain labels	KB, MB, GB, TB interpreted in legacy mode	1024

Accepted size values range from 0 to 1,000,000,000,000 in the selected unit. File count ranges from 1 to 1,000,000,000 whole files. Display precision affects presentation only and may be set to 2, 3, 4, or 6 decimal places.

Worked Examples:

Vendor 1 TB drive label

A decimal 1 TB label equals 1,000,000,000,000 bytes. Dividing by 1024³ gives about 931.323 GiB. With a 10% reserve, the planning model treats 900,000,000,000 bytes as usable before any allocation or file-system-specific effects are considered.

References:

NIST Guide to the SI, Chapter 4, National Institute of Standards and Technology.
Prefixes for Binary Multiples, National Institute of Standards and Technology.
How to configure Elasticsearch disk watermarks, Simplified Guide.