Spaces between letters in Morse code: gaps, timing and how to write them

The international standard, ITU-R M.1677-1, sets every length in dots. Its rules are four short lines:

• Dash: "A dash is equal to three dots".
• Inside a letter: the space between the signals of one letter "is equal to one dot".
• Between letters: "the space between two letters is equal to three dots".
• Between words: "the space between two words is equal to seven dots."

Because every length is counted in units, the rule holds at any speed. A unit lasts 1200 divided by the speed in words per minute, in milliseconds: 66.7 ms at 18 WPM, 60 ms at 20 WPM. That number comes from the standard word PARIS, which is exactly 50 units long with the word gap after it.

Here is how the 111 units of HELLO WORLD add up, counted by the site's own code:

• HELLO WORLD

  .... . .-.. .-.. --- / .-- --- .-. .-.. -..111 units · 7.40 s

At 18 WPM that is 7.40 seconds. Almost half of it, 53 of the 111 units, is silence. The gaps are not dead time; they carry the structure of the message.

Morse code has no end-of-letter signal. Only the length of the silence tells the listener that a letter is over. Run the letters together and the same dots read as other letters:

This is why a message written without spaces is so hard to read back: six dots in a row could be any of the lines above, or several others. If you do have Morse with the letter gaps lost, the Morse decoder without spaces reads them as ranked guesses.

The ITU standard times the gaps but says nothing about writing them down. The common written form, and the one this site uses, is:

• one space between letters, as in .. / .-.. --- ...- . / -.-- --- ..- for I LOVE YOU;
• a slash between words, with a space on each side;
• a new line between sentences, if you like.

The translators on this site read one or two spaces as a letter gap, and a slash, a vertical bar, a new line, a tab or three or more spaces as a word gap. So you can paste Morse in any of the first three forms into Morse code to English and get the same words back.

Farnsworth spacing sends each letter at full speed but stretches the gaps between letters and words, so a learner hears the true rhythm of every letter and still has time to think. The extra time is shared out by a formula ARRL published in 1990: three parts to each letter gap and seven parts to each word gap, the same 3 to 7 ratio as normal spacing.

The translator's Timing panel has a Farnsworth switch. It slows the overall speed to anything from 5 WPM up to one below the letter speed, and starts at 13 WPM when you turn it on. With letters at 18 WPM, the gaps grow like this:

The dots and dashes stay at 66.7 and 200 ms in every row; only the silences change. A separate switch, Extra word spacing, stretches only the word gaps, from 1.5 to 4 times (2 times, 933 ms, when first turned on).

The seven-unit word gap is younger than the code. The ITU's Telegraph Regulations of 1938 still set "the space between two words" at five dots; the 1949 revision made it seven, the value in today's standard.

American Morse, the original landline code, has an extra gap: some of its letters, such as C, O, R, Y and Z, contain a short space inside the letter itself. That is one reason it is hard to copy for anyone trained on International Morse. You can hear the spaced letters in American Morse code.

Type a sentence into the translator, press Play and listen for the gaps, then open Timing and switch on Farnsworth to hear them stretch.

To train your ear on letter and word gaps at full speed, copy real words in CW listening practice.