Morse Code Translator

This is International Morse code as defined by the ITU in Recommendation M.1677-1. Morse has no capital or small letters, so decoding always gives capitals. A dot is written . and a dash -.

Numbers follow a pattern: every digit is five signals. 1 to 5 are that many dots followed by dashes, and 6 to 9 are (digit − 5) dashes followed by dots. 5 is five dots and 0 is five dashes.

Morse is a rhythm, and everything is measured in one unit, the length of a dot. The ITU standard fixes the rest as multiples of it. Those gaps are what written Morse shows with spaces and slashes, which is why the spacing matters so much when you write it down.

Speed is measured in words per minute using the word PARIS, which takes exactly 50 units including the gap after it. At 20 wpm that is 1,000 units a minute, so one unit lasts 60 ms. In general a dot lasts 1,200 ÷ wpm milliseconds.

Worked example. SOS sent as three letters is S (5 units) + gap (3) + O (11) + gap (3) + S (5) = 27 units, or 1.62 s at 20 wpm. Sent the proper way, as one prosign with no gaps between letters, it is 23 units, 1.38 s. Type both SOS and <SOS> above and play them to hear the difference; the status line shows each length.

Sent slowly, Morse letters stretch out until each one is a string of separate beeps you end up counting. Farnsworth spacing avoids that: the letters keep the sound they have at a normal speed, and only the gaps between letters and words get longer. Set Speed to the letter speed and Overall speed in Fine-tune to the slower pace you can keep up with.

The standard formula, from Jon Bloom’s 1990 ARRL paper, comes from PARIS: 31 of its 50 units are sound and 19 are spacing. With letters at c wpm and an overall speed of s wpm, the total extra spacing per word is t = (60c − 37.2s) ÷ (c·s) seconds, split as 3t/19 between letters and 7t/19 between words.

Worked example. Letters at 18 wpm with an overall speed of 5 wpm: t = (1,080 − 186) ÷ 90 = 9.93 s, so the gap between letters is 1.57 s and between words 3.66 s, while a dot is still a crisp 67 ms. PARIS then takes exactly 12 seconds, which is 5 words a minute.

Learn each letter as a sound, not a picture. “Dah-di-dah-dit” is C; reading -.-. off a chart and counting is the habit that stalls people at about 10 wpm. The Koch method, from the German psychologist Ludwig Koch in the 1930s, starts with just two letters at full speed and adds one each time you copy 90% correctly.

A prosign is a procedural signal: two or three letters run together as one character, with no gap between them. They are written with angle brackets or a bar over the letters. SOS is the famous one. It does not stand for “save our souls”; the pattern was chosen because three dots, three dashes, three dots is impossible to mistake, and it became the international distress signal at the 1906 Berlin radiotelegraph conference.

Several prosigns share a pattern with a punctuation mark, so .-.-. could be a plus sign or the end of a message. The translator decodes those as the character and only shows a prosign, such as <SOS> or <SK>, when the pattern means nothing else. Ships stopped keeping a Morse distress watch when the Global Maritime Distress and Safety System took over on 1 February 1999.

Pasted Morse comes in many forms, and the translator accepts most of them. It decides by itself whether the box holds text or Morse; if it guesses wrong, for example with a single ..., set Read the box as in Fine-tune.

The one thing a decoder cannot fix is missing letter gaps. Without spaces, Morse is ambiguous because short codes are the start of longer ones: . is E, .. is I, ... is S. Written as ...---..., SOS can be split into letters A to Z in 192 different ways, from SOS to EEETTTEEE. HELLO without gaps, ......-...-..---, has 19,796 readings. That is why the gap between letters is three units long on air, and why a space belongs between every letter on paper.

The ITU table has only one accented letter, É. Other languages added their own, and the translator uses these widely recognised ones. Any other accented letter is sent as its plain letter, as operators do, and the status line says so. Characters with no code at all, such as # or emoji, are left out and listed. ß is sent as SS.

The ITU writes some symbols as sequences instead: % is sent as 0/0 and the multiplication sign × is the same as X, which is how the translator handles ×.

International Morse is not quite the code Samuel Morse and Alfred Vail used on the first US telegraph line in 1844. That original, now called American or Railroad Morse, had gaps inside some letters (C was .. . and O was . .) and a long dash for L. Friedrich Gerke simplified it for German telegraphs in 1848, and his version became the international standard from 1865. American Morse lasted on US railways and landlines well into the 20th century; this page uses the international code only.