Random letter-and-number sets are handy anywhere you need a short code nobody can guess or predict: raffle ticket IDs, classroom group labels, scavenger-hunt clues, invite codes, test data or the starting letters for a word game. Choose which characters may appear and how long each set should be, and the generator builds as many sets as you need.
How to use the generator
- Choose the characters: letters and numbers, letters only, or numbers only.
- For letters, pick capitals, lowercase or mixed case.
- Set the characters per set (1–64) and the number of sets (up to 500).
- Tick No repeated characters if a set may not use the same character twice.
- Leave look-alike characters removed for codes people will read or type, then press Generate.
The tape reports the size of the character pool, how many different sets are possible and the strength of each set in bits.
How many codes are possible?
Each character is chosen independently from a pool of N symbols, so a set of length L has
With No repeated characters, the count drops to a permutation: N × (N − 1) × … × (N − L + 1).
| Character pool | Pool size | 4 characters | 6 characters | 8 characters |
|---|---|---|---|---|
| Digits 0–9 | 10 | 10,000 | 1,000,000 | 100,000,000 |
| Capitals A–Z | 26 | 456,976 | 308,915,776 | ≈ 2.09 × 10¹¹ |
| Capitals + digits, no look-alikes | 32 | 1,048,576 | 1,073,741,824 | ≈ 1.10 × 10¹² |
| Capitals + digits | 36 | 1,679,616 | 2,176,782,336 | ≈ 2.82 × 10¹² |
| Both cases + digits | 62 | 14,776,336 | ≈ 5.68 × 10¹⁰ | ≈ 2.18 × 10¹⁴ |
Each extra character multiplies the possibilities by the pool size, so length matters far more than the choice of pool.
Worked example: 200 check-in codes for an event
You need 200 codes that volunteers will read from a badge and type into a sign-in sheet.
- Choose letters and numbers, capitals only, look-alikes removed: a 32-character pool.
- Five characters give 32⁵ = 33,554,432 possible codes, about 25 bits each.
- The chance that a random guess matches one of your 200 codes is 200 ÷ 33,554,432 ≈ 0.0006%.
Generate 200 sets, paste them into a spreadsheet, and check for duplicates there before printing. With 200 five-character codes the chance of any duplicate is about 0.06%, so you will almost never see one.
Look-alike characters
Printed codes fail most often because of characters that look the same: zero and capital O, one and capital I or lowercase l. Removing those five keeps 24 capital letters, 8 digits and (in mixed case) 25 lowercase letters. The pool for capitals plus digits goes from 36 to 32 — a small loss you can recover with one extra character.
Ideas and uses
- Word games: generate four capital letters and race to make the longest word using them.
- Labels and IDs: tag samples, storage bins or test accounts with short unique codes.
- Teaching probability: compare how fast NL grows for different pools and lengths, then check the count with the permutations with replacement calculator.
- Codes for games: secret words, treasure-hunt clues or escape-room locks.
For numeric codes only, the PIN generator also filters out guessable patterns like 1234. For account passwords use the password generator, which is designed for longer, stronger secrets.
Every character is chosen with your browser's cryptographic random generator and nothing is sent to a server. Treat codes as unguessable only if they are long enough for how they will be used.
Frequently asked questions
How many different codes can this generator make?
It is the pool size raised to the code length. With 32 characters (capital letters and digits, look-alikes removed) and 6 characters per set there are 32⁶ = 1,073,741,824 possible codes.
Why leave out 0, O, 1, I and l?
They are easy to confuse when a code is printed, read aloud or typed from a label. Removing them shrinks the pool slightly but prevents most transcription mistakes.
Can two sets in one batch be identical?
It is possible but very unlikely for long codes. With six characters from a 32-character pool, 100 codes have roughly a 0.0005% chance of containing a duplicate. Use longer sets if you need many codes.
Should I use these sets as passwords?
Short sets are fine for low-stakes codes, but passwords should be longer and mix more character types. Use a dedicated password generator for account passwords.