Letter Frequency Counter
Paste a text and the counter shows how many times each letter from A to Z appears, the share of all letters, and a bar chart with a mark for the usual English frequency. It also gives the index of coincidence and a chi-square distance from English, the two measures cryptographers use to tell English from a substitution or Vigenere cipher, and the share of vowels. Everything runs in your browser.
The index of coincidence is close to English (about 0.067). This looks like ordinary English, or a cipher that keeps letter frequencies, such as a simple substitution or a Caesar shift.
| Letter | Count | Yours | English | Yours (bar) and English (mark) |
|---|---|---|---|---|
| E | 17 | 13.2% | 12.7% | |
| T | 17 | 13.2% | 9.1% | |
| S | 14 | 10.9% | 6.3% | |
| I | 13 | 10.1% | 7.0% | |
| O | 12 | 9.3% | 7.5% | |
| H | 9 | 7.0% | 6.1% | |
| A | 8 | 6.2% | 8.2% | |
| F | 8 | 6.2% | 2.2% | |
| W | 8 | 6.2% | 2.4% | |
| C | 3 | 2.3% | 2.8% | |
| L | 3 | 2.3% | 4.0% | |
| M | 3 | 2.3% | 2.4% | |
| B | 2 | 1.6% | 1.5% | |
| D | 2 | 1.6% | 4.3% | |
| G | 2 | 1.6% | 2.0% | |
| N | 2 | 1.6% | 6.7% | |
| P | 2 | 1.6% | 1.9% | |
| R | 2 | 1.6% | 6.0% | |
| U | 1 | 0.8% | 2.8% | |
| Y | 1 | 0.8% | 2.0% | |
| J | 0 | 0.0% | 0.2% | |
| K | 0 | 0.0% | 0.8% | |
| Q | 0 | 0.0% | 0.1% | |
| V | 0 | 0.0% | 1.0% | |
| X | 0 | 0.0% | 0.1% | |
| Z | 0 | 0.0% | 0.1% |
Only the letters A to Z are counted, upper and lower case together, and accented letters count as their base letter. The English figures are the "Texts" column of the Wikipedia letter frequency table, which comes from Lewand's Cryptological Mathematics, scaled to add up to 100. The index of coincidence is the chance that two letters picked from the text are equal: about 0.0667 for English and 0.0385 for random letters. A short text gives rough numbers, so use a few hundred letters or more. Everything runs in your browser.
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Analysis & CountingAbout the Letter Frequency Counter
Letters are not equally common in English. Wikipedia's letter frequency table, which comes from Lewand's Cryptological Mathematics, lists E at 12.7%, T at 9.1% and A at 8.2%, with Z, Q, X and J below 0.2% each. The counter counts only the letters A to Z, ignoring case, and treats accented letters as their base letter. The index of coincidence is the chance that two letters picked at random from the text are the same. For English it is about 0.067, and for random letters it is 1/26, or 0.0385. A simple substitution cipher or a Caesar shift keeps the letter pattern, so its index stays near 0.067, while a Vigenere cipher mixes several alphabets and pulls the index towards 0.0385. The chi-square value measures how far the letter counts are from English proportions, with 25 degrees of freedom, and lower means closer. Short texts give noisy results, so use a few hundred letters or more for a firm reading.
What is the most common letter in English?▾
E, at about 12.7% of letters according to Lewand's table, followed by T at 9.1% and A at 8.2%.
What is the index of coincidence?▾
It is the chance that two letters picked at random from a text are the same. It is about 0.067 for English and 0.0385 for random letters.
How does letter frequency help break a cipher?▾
A simple substitution cipher keeps the frequency pattern, so the most common ciphertext letter probably stands for E. A flatter pattern points to a polyalphabetic cipher such as Vigenere.
Does it count digits, spaces and punctuation?▾
The chart counts only the letters A to Z. Digits, spaces and other characters are tallied separately and left out of the percentages.
Is my text uploaded?▾
No. The counting runs in your browser and your text is not sent anywhere.