O in Morse Code: Three Dashes (---)

O is the dash-only partner of S (...), and the pair forms the middle of the SOS distress signal. Below you will find how to write, hear, time and send O, plus the signals beginners most often mistake for it.

How to write O in Morse code

To write O in Morse code, draw three dashes of equal length with a small, even space between them: --- (the O pattern). Keep the dashes clearly longer than a dot would be, because a hurried "three short lines" on paper is easy to misread.

When you type it, three hyphens are the usual stand-in for the dashes. A few rules keep a written message readable:

• Leave one space after the O before the next letter, for example -. --- for NO.
• Mark a word break with a wider gap or a slash, a common convention in typed Morse.
• Never join O to its neighbor: ---- is a different character (CH in extended Morse), not O plus a dash.

What O sounds like

O sounds like three steady, identical tones: dah, dah, dah. Operators say "dah" for every dash and "dit" or "di" for dots, and O has no dots, so the rhythm never changes inside the letter.

That evenness is what your ear locks onto. The tones are the same length, the two silences inside the letter are the same length, and the letter ends with a longer pause before whatever comes next.

How long O takes to send

Every Morse element is measured in units. A dash lasts 3 units, the gap inside a letter lasts 1 unit, the gap between letters lasts 3 units, and the gap between words lasts 7 units, as set in the ITU standard.

O therefore takes 11 units on its own. Using the PARIS standard, one unit in milliseconds equals 1200 divided by the speed in words per minute (WPM):

For comparison, E takes 1 unit and T takes 3. O is one of the longer letters to send, even though it is a frequently used vowel.

How to send O with a key, light or sound

You send O by holding the signal on three times for 3 counts each, with 1 count off between them. The method is the same on a telegraph key, a flashlight, a whistle or a car horn.

1. Pick a steady count for one unit, such as a quick "one."
2. Turn the signal on and hold it for three counts.
3. Turn it off for one count.
4. Repeat: on for three, off for one, on for three.
5. Stay silent for three counts before the next letter, or seven before the next word.

On a straight key, beginners tend to clip dashes until they sound like dots. If your O starts sounding like S, slow down and stretch each dash.

Signals people confuse with O

Most O mistakes come from miscounting dashes or misjudging the gaps between them. This table lines up the patterns that look or sound closest to O:

The TTT row is the subtle one. Its three dashes are spaced as three separate letters, which is exactly how it stays distinct from O, so the silence between dashes matters as much as the dashes themselves.

O and S: the pair inside SOS

O is the exact opposite of S: three dashes against three dots. SOS strings them together as three dots, three dashes, three dots (...---...).

SOS first appeared in German maritime radio rules that took effect on April 1, 1905. It became the world standard through the International Radiotelegraph Convention signed in Berlin on November 3, 1906, effective July 1, 1908.

Two details are often wrong elsewhere. SOS is sent as one unbroken sequence with no letter gaps, and it was never an abbreviation: "save our souls" and "save our ship" are later backronyms. You can learn the full signal on our SOS in Morse code page.

Is O always three dashes?

In International Morse, yes, but other Morse systems used or reuse the same pattern differently. This matters if you read historical telegrams or switch between alphabets.

Because American operators read three dashes as 5, some early U.S. reports wrote the distress call as "S 5 S."

Common words with O in Morse code

Seeing the Morse code for O inside real words trains your eye to spot the three-dash block quickly. Letters are separated by a space here:

In ZOO, the two O's sit side by side, and only the 3-unit letter gap separates them. Listen for it, or the six dashes blur into one long run.

How to remember O

The fastest way to remember O is to count dashes: T is one, M is two, O is three. That mirrors the dot side, where E is one dot, I is two and S is three.

• Learn O and S together, since they are exact opposites and appear together in SOS.
• Picture the dash ladder from the code-order charts used by radio clubs: T, M, O.
• Learn by sound, not by sight. The Koch method teaches characters at full speed, adding a new one only after you copy the current set with 90% accuracy.

Once three dashes feel automatic, compare O with its neighbors in the Morse code alphabet, starting with S in Morse code and M in Morse code. You can also type any word into the Morse code translator to hear where O falls.