How letter numbers work
The simplest number code gives each letter its place in the alphabet: A is 1, B is 2, C is 3 and so on up to Z, which is 26. It is often called A1Z26. HELLO becomes 8-5-12-12-15.
In this tool the numbers for each word are joined with hyphens and words are separated by spaces, but when decoding you can use spaces, commas, hyphens or slashes; the tool works it out. Tick Start at A = 0 if your puzzle counts from zero, which is common in computing and some maths puzzles.
Where you will find letter numbers
Letter numbers turn up in escape rooms, geocaching, treasure hunts, birthday cards and children's puzzle books. They are also a building block for other codes: many puzzle setters turn letters into numbers first and then add or multiply them to hide the message further.
To write a message by hand, a quick trick is to remember a few landmarks: E is 5, J is 10, O is 15, T is 20 and Y is 25. Count on or back from the nearest one.
If a code uses numbers above 26, it may be ASCII, where capital A is 65, or it may be a book cipher, where numbers point to words in a particular book. The cipher decoder can help you tell which.
Questions and answers
What number is each letter?
A = 1, B = 2, C = 3, D = 4, E = 5 and so on to Z = 26. The chart under the tool shows them all.
How should I separate the numbers?
Any way you like. Hyphens, commas or spaces between letters all work; leave a space or a slash between words.
What does A = 0 mean?
Some puzzles number the alphabet from zero, so A is 0 and Z is 25. Tick the box to use that system.
What happens to numbers above 26?
They are not letters in this code, so they are shown as a question mark and listed under the result.