Tap Code Translator
Each letter is two numbers: the row, then the column. K is sent as C. Separate words with a slash.
Type a message to get the tap code for it, or enter number pairs like 23 15 to decode them. Press play to hear it as knocks on a wall.
People often search for "tapping Morse code" when they mean this. Tap code is its own system, and it's a lot easier to send by knocking than Morse is. If you do want real Morse, the main translator handles that, and you can tap out dots and dashes with our Morse code keyboard.
The tap code grid
Every letter lives in a 5x5 square. You tap the row number, pause, then tap the column number. There are only 25 cells, so K is sent as C.
| 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|
| 1 | A | B | C/K | D | E |
| 2 | F | G | H | I | J |
| 3 | L | M | N | O | P |
| 4 | Q | R | S | T | U |
| 5 | V | W | X | Y | Z |
So H is row 2, column 3: two taps, a pause, three taps. W is five taps then two. Those are the same examples PBS gives in its history of the code.
"HELLO" comes out as 23 15 31 31 34.
How to send tap code
- Find your letter's row and tap that many times.
- Pause for a beat.
- Tap the column number.
- Leave a longer pause before the next letter.
You don't need to remember the whole grid. If you know the first letter of each row (A, F, L, Q, V), you can count across to anything else.
Where tap code came from
The idea is very old. It comes from the Polybius square, a Greek system for signaling letters with torches, where one set of torches gave the row and the other gave the column. Political prisoners in Tsarist Russia are said to have knocked a version of it through cell walls, and Arthur Koestler wrote about it in his 1941 novel Darkness at Noon (overview on Wikipedia).
The Vietnam POWs and the "Hanoi Hilton"
Tap code is best known from the Vietnam War. Air Force Capt. Carlyle "Smitty" Harris had heard about it from an instructor at survival school in Nevada before he deployed, as the Army University Press notes in its review of his memoir. After he was shot down in April 1965 and taken to Hỏa Lò prison, he and fellow prisoners Phillip Butler, Robert Peel and Robert Shumaker started spreading it in June 1965. Within a couple of months most of the prisoners there had learned it (PBS).
The prisoners got creative. They held tin cups to the walls to hear better, and some sent the code with coughs, sniffs and broom sweeps in the yard. Rep. Sam Johnson, a former POW, called his cup "a lifeline" (Smithsonian Magazine). Harris spent nearly eight years as a prisoner before coming home in 1973 and published a memoir called Tap Code in 2019 (Air & Space Forces Magazine).
Common tap code abbreviations
To save time, the POWs cut common phrases down to a few letters:
| Tapped | Meaning |
|---|---|
| GN | Good night |
| ST | Sleep tight |
| GBU | God bless you (the usual sign-off) |
| X | End of sentence |
The PBS feature lists these along with others, and the National Veterans Memorial and Museum explains that X split sentences and a "shave and a haircut" knock opened a conversation.
Tap code vs Morse code
| Tap code | Morse code | |
|---|---|---|
| Symbols | Groups of 1 to 5 identical taps | Short and long signals (dots and dashes) |
| Hard part | Counting | Telling a short signal from a long one by rhythm |
| Speed | Slower, up to 10 taps per letter | Faster once learned |
| Best for | Knocking, tapping, anywhere length is hard to show | Sound, light and radio |
A knock on a wall is always the same length, so you can't really make a "long" tap. That's probably why counting worked better than Morse inside a prison. If you do want to tap Morse, here's how to tap Morse code so long and short taps stay readable. Tap code is slower, but it's easier to learn and works in more situations. If you're signaling with a flashlight or a buzzer, Morse is the better fit. Try the light translator or the audio translator for that.
Frequently asked questions
Is tap code the same as Morse code? No. Tap code uses a 5x5 letter grid and counts taps, while Morse code uses short and long signals. They're both ways to spell letters with simple signals, but the codes don't match.
Why is there no K in tap code? The grid has 25 cells and the alphabet has 26 letters, so one letter has to share. In the standard version, K uses the C cell, and you figure it out from context.
What does GBU mean in tap code? God bless you. Vietnam POWs used it to sign off at the end of a conversation.
How do you say SOS in tap code?
S is 43 and O is 34, so SOS is 43 34 43. For the Morse version, see SOS in Morse code.
Who invented tap code? The grid goes back to the Polybius square in ancient Greece. Its most famous modern use began in 1965 when Smitty Harris and fellow POWs taught it to prisoners in Hanoi.
Related: military Morse code · Morse code keyboard · light translator · main translator