What Is a GUID — and How Is It Different from a UUID?
A GUID (Globally Unique Identifier) is Microsoft's implementation and name for a UUID — a 128-bit identifier in the same 8-4-4-4-12 hexadecimal format. In practice the terms are interchangeable: "GUID" is common in the Microsoft/.NET world, while "UUID" is used everywhere else. They describe the same thing.
If you've wondered whether a GUID and a UUID are different, here's the short and complete answer.
What Is a GUID?
A GUID is a 128-bit value used to uniquely identify something without a central registry:
3F2504E0-4F89-41D3-9A0C-0305E82C3301
Microsoft adopted "GUID" for its platforms (COM, the Windows Registry, SQL Server, .NET), but the underlying concept and bit layout are exactly the same as a UUID. Generate one with our UUID Generator — the output is identical in format and works wherever a GUID is expected.
GUID vs UUID: Are They the Same?
For all practical purposes, yes. Both are:
- 128 bits long
- Written as 32 hex digits in the 8-4-4-4-12 pattern
- Designed to be globally unique without coordination
"UUID" comes from the formal standard (RFC 4122, now RFC 9562); "GUID" is Microsoft's term for its implementation of that standard. A UUID generated by a Linux service and a GUID generated by .NET are the same kind of value.
The Minor Differences
There are a few cosmetic/historical quirks:
| GUID (Microsoft) | UUID (standard) | |
|---|---|---|
| Origin | Microsoft platforms | RFC 4122 / 9562 |
| Common casing | Often UPPERCASE | Usually lowercase |
| Braces | Often wrapped in {...} |
Bare |
| Historical quirk | Some legacy GUIDs didn't follow RFC version/variant bits exactly | Always RFC-conformant |
These are formatting and convention differences, not structural ones. A modern .NET Guid.NewGuid() produces a perfectly valid version-4 UUID.
Where "GUID" Is Used
You'll see the term "GUID" most often in:
- .NET / C# — the
System.Guidtype. - SQL Server — the
UNIQUEIDENTIFIERcolumn type. - Windows Registry & COM — class IDs (CLSIDs) and interface IDs.
- Office / VBA — object identifiers.
Outside Microsoft ecosystems (Postgres uuid, Java UUID, JavaScript crypto.randomUUID()), you'll see "UUID."
Which Should You Use?
Use whichever term matches your platform — they produce compatible values. For the full breakdown of versions (v1, v4, v7) and uniqueness guarantees that apply to both, see What Is a UUID? and UUID v4 vs UUID v7. Generate values in this format with our UUID Generator.
Frequently Asked Questions
What is a GUID? A 128-bit globally unique identifier — Microsoft's name and implementation of a UUID — written as 32 hex digits in the 8-4-4-4-12 format.
Is a GUID the same as a UUID? Effectively yes. They share the same size and format; "GUID" is Microsoft's term and "UUID" is the standard's term for the same concept.
What does GUID stand for? Globally Unique Identifier.
What's the difference between GUID and UUID? Mostly conventions: GUIDs are often uppercase and brace-wrapped in Microsoft tooling, while UUIDs are typically lowercase and bare. Structurally they're the same.
Where are GUIDs used?
In Microsoft technologies like .NET (System.Guid), SQL Server (UNIQUEIDENTIFIER), the Windows Registry, and COM.
Related Reading
Bottom line: GUID and UUID are two names for the same 128-bit identifier. Pick the term your stack uses and don't worry — the values are interchangeable.