What is O in Morse code?

O is three dashes (−−−). It is the longest all-dash letter of the basic alphabet; a fourth dash takes you out of the ITU letters to CH (−−−−), used in some other languages.

What part of SOS is O?

O supplies the three dashes in the middle of ···−−−···. Because SOS is keyed as one signal, the O is not set apart by letter gaps; it sits between the two runs of dots like the long middle of a phrase.

Was O different in American Morse?

Yes. In the American landline code O was two dots with a space between them (· ·). International code uses three dashes, which leaves no chance of hearing it as two E’s.

The Letter O in Morse Code

O is −−−: no short di and 3 long dahs, dah-dah-dah. It lasts 11 units.

−−−dah-dah-dah

O drawn to time: 11 units, then a 3-unit gap before the next letter.

SpeedSlow · 8 WPMNormal · 18 WPMFast · 25 WPM

Facts about O

Code: −−− · dah-dah-dah
Elements: 3 — no dot, 3 dashes
Length: 11 units + 3 before the next letter
Time: 0.66 s at 20 WPM · 1.65 s at 8 WPM
Tree: T → M → O · a leaf: no sign below it
Frequency: 7.64% of English letters, 4th of 26²
Koch order: 19th sign of the course
Spelling: Oscar
Same signal: О in Russian Morse · Ο in Greek Morse · レ in Wabun

§ 1Don’t confuse O with

Othis letterdah-dah-dah
Mone element shorterdah-dah
Wfirst element differsdi-dah-dah
Kelement 2 differsdah-di-dah
Glast element differsdah-dah-dit
Jone element longerdi-dah-dah-dah
Yone element longerdah-di-dah-dah
Qone element longerdah-dah-di-dah
Smirror: every di and dah swappeddi-di-dit

Blue marks the elements that differ from O.

§ 2How to remember O

OH-SO-SLOW (−−−) — O mirrors S (···): three long dahs against three short dits, the middle of SOS.

§ 3Words with O

§ 4Questions about O

What is O in Morse code?: O is three dashes (−−−). It is the longest all-dash letter of the basic alphabet; a fourth dash takes you out of the ITU letters to CH (−−−−), used in some other languages.
What part of SOS is O?: O supplies the three dashes in the middle of ···−−−···. Because SOS is keyed as one signal, the O is not set apart by letter gaps; it sits between the two runs of dots like the long middle of a phrase.
Was O different in American Morse?: Yes. In the American landline code O was two dots with a space between them (· ·). International code uses three dashes, which leaves no chance of hearing it as two E’s.