CUID2 collision calculator
Shorter IDs are nicer in URLs, until two collide. Set the length and how many IDs you expect, and see the odds of a duplicate.
2 to 32; the default is 24
Every id you'll ever create in that table
Distinct IDs
1.62 × 1037
50% chance of a duplicate at
4.74 × 1018 IDs
Your chance of a duplicate
1 in 3.24 × 1025
Under one in a million: safe.
Chance of any duplicate, by length
| Length | 10 thousand IDs | 1 million IDs | 100 million IDs | 10 billion IDs |
|---|---|---|---|---|
| 8 | 1 in 40,754 | 21.76% (1 in 5) | 100.0% | 100.0% |
| 10 | 1 in 5.28 × 107 | 1 in 5,282 | 84.9% | 100.0% |
| 12 | 1 in 6.85 × 1010 | 1 in 6.84 × 106 | 0.15% (1 in 685) | 100.0% |
| 16 | 1 in 1.15 × 1017 | 1 in 1.15 × 1013 | 1 in 1.15 × 109 | 1 in 114,959 |
| 20 | 1 in 1.93 × 1023 | 1 in 1.93 × 1019 | 1 in 1.93 × 1015 | 1 in 1.93 × 1011 |
| 24 | 1 in 3.24 × 1029 | 1 in 3.24 × 1025 | 1 in 3.24 × 1021 | 1 in 3.24 × 1017 |
| 32 | 1 in 9.15 × 1041 | 1 in 9.15 × 1037 | 1 in 9.15 × 1033 | 1 in 9.15 × 1029 |
How to use it
- Set the CUID2 length you use (24 is the default; createId({ length }) changes it).
- Enter how many IDs you’ll ever create.
- Read the probability, and check the table for the shortest safe length.
Questions
How is it calculated?+
A CUID2 starts with a letter (26 options) followed by base-36 characters, so a length-L ID has 26 × 36^(L−1) values. The birthday bound gives the chance of any duplicate among n IDs: 1 − e^(−n(n−1)/2N).
What probability is safe?+
A common bar is under one in a million over the table’s lifetime. If a collision would be costly, keep a unique index so a duplicate fails loudly.
More free tools
Sitemap Viewer
Load any XML sitemap and browse its URLs as folders.
URL Parser
Split any URL into host, path, query parameters and fragment.
Connection Request Generator
Six connection notes under 300 characters, written for one person.
LinkedIn Message Generator
A first DM and two follow-ups that sound like a person, not a sequence.
ICP Generator
Your ideal customer profile: titles, pains, buying signals, who to skip.
Social Listening Keyword Generator
Phrases people post when they need what you sell, plus subreddits and negatives.
LinkedIn Headline Generator
Twelve headlines under 220 characters that make prospects click.
LinkedIn Profile Review
A score out of 100, the fixes that matter and a rewritten headline and About.
Free Lead Report
The people who need what you sell this week, by name.
Every mention on LinkedIn, X and Reddit, for $49 a month.
Track your brand, competitors and category across LinkedIn, X/Twitter, Reddit, Bluesky and Hacker News. AI scores each post for relevance and sentiment, and the ones worth acting on reach Slack, Discord or email.
The cheapest LinkedIn + X + Reddit monitoring with AI scoring and Slack alerts
| Updately | $49/mo |
| KWatch.io | $79/mo |
| Octolens | $199/mo |
| Brandwatch | $800+/mo |
- 10-day free trial
- Paid plans: 10-day free trial · $39/mo billed annually
Run it from Claude
Add Updately as a custom connector in Claude (or ChatGPT, Cursor, any MCP client) and work in plain English. MCP setup guide
https://api.updately.ai/mcpYou ask Claude
“What did people say about our competitors on Reddit and X this week? Draft replies to the three best threads.”
“Updately gave us control of what we were doing as opposed to giving the keys and letting them go. But most importantly, the reason why we joined Updately was because it was a third of the price of the agency that we were using to do a similar type of outreach.”
“If you don't have an active, engaged LinkedIn pipeline and you have a clearly defined ICP and persona, you need to add Updately to your tech stack immediately to supplement your sales.”
“I found myself looking at some of the messages that it's created and thinking like, wow, where did it find this? This went really deep to find information that you could never do in just a cursory search.”