UUID v4 & ULID Generator — Generate Unique Identifiers
Generate random UUID v4 and ULID identifiers instantly. Bulk generate multiple IDs, copy to clipboard, and choose between UUID and ULID formats.
UUID Generator
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736319d5-8349-41f1-88f2-8286894b0ea4Click to copyb6e40a6c-7605-4cd7-9652-9e1bf0db46d2Click to copyd9ac035a-7238-4eac-bd0d-54d148bcbce4Click to copyebb3139b-2c0b-46d9-acb7-81d190dfe982Click to copya69ba3b5-44c7-4b97-9420-ba4c91785827Click to copyThe Formula
UUID v4 (Universally Unique Identifier version 4) generates a 128-bit random identifier displayed as 36 hexadecimal characters in the format 8-4-4-4-12. ULID (Universally Unique Lexicographically Sortable Identifier) is a 26-character Crockford base32-encoded identifier where the first 10 characters encode a 48-bit millisecond timestamp and the last 16 characters are random, making ULIDs time-sortable.
Variable Definitions
UUID Version 4
A 128-bit randomly generated identifier with 122 bits of randomness and 6 fixed variant/version bits. 5.3 x 10^36 possible values.
Universally Unique Lexicographically Sortable Identifier
A 26-character Crockford base32 encoded identifier with a 48-bit timestamp prefix and 80-bit random suffix. Sortable by creation time.
Crockford Base32 Encoding
An encoding scheme using 32 unambiguous characters (0-9, A-Z excluding I, L, O, U) to represent 5 bits per character. Used by ULID for compact, URL-safe representation.
Identifier Collision
The probability that two randomly generated identifiers are the same. UUID v4 collision probability is approximately 1 in 2^71 for 10^18 UUIDs generated.
How to Use This Calculator
- 1
Select the format: UUID v4, ULID, or Both to compare formats side by side.
- 2
Enter the number of IDs to generate (1 to 50). Multiple IDs are separated by commas.
- 3
Review the generated IDs and copy them for use in your application.
- 4
UUID v4 IDs are fully random; ULIDs are prefixed with the current timestamp for time-sortable ordering.
- 5
Generate multiple IDs in bulk for seeding databases or populating test data.
Quick Reference
| From | To |
|---|---|
| UUID v4 Format | xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx |
| ULID Format | TTTTTTTTTTRRRRRRRRRRRRRRRR (10T + 16R) |
| UUID v4 Entropy | 122 random bits (approx. 5.3 x 10^36 values) |
Common Applications
- Generating primary keys for database records that need to be unique across distributed systems.
- Creating unique session identifiers and API tokens for web applications.
- Generating order numbers and transaction IDs that need to be sortable by creation time (ULID).
- Producing unique identifiers for microservices communication where centralized ID generation is impractical.
- Populating test databases with realistic, unique identifier values for development and QA.
UUID v4 generates random 128-bit identifiers; ULID combines timestamp prefix with random suffix for time-sortable IDs
Understanding the Concept
Universally Unique Identifiers (UUIDs) and ULIDs serve the critical purpose of generating unique identifiers without requiring a central authority. UUID v4 is purely random: each of its 122 random bits (out of 128 total) is independently generated, making collisions astronomically unlikely. The version (4) and variant bits are fixed at positions 13 and 17 respectively. ULID was designed as a modern alternative that brings time-sortability to unique IDs: the first 10 characters encode a 48-bit millisecond timestamp using Crockford Base32, allowing ULIDs to be lexicographically sorted by creation time. This makes ULIDs particularly useful for database indexing where B-tree performance benefits from insertion-time ordering. ULIDs use Crockford Base32 encoding which excludes ambiguous characters (I, L, O, U) for human readability and case-insensitive processing. Both UUID v4 and ULID are 128-bit identifiers, but ULID is more compact at 26 characters vs 36 characters for UUID v4. The timestamp prefix in ULID provides approximately 1 millisecond precision and will not overflow until the year 10889.
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