What is a single dash in morse code?

A single dash is the letter T. It is one dah, the long signal, which lasts exactly three times as long as a dit. T and E are the only characters in ITU-R M.1677-1 that are a single mark.

One dah, played on its own. At 20 WPM it lasts 180 milliseconds, against 60 for a single dit.

Why T is a single dah

ITU-R M.1677-1 builds every character out of two marks and nothing else: the dit, one unit long, and the dah, three units long. T is the whole of the second one. E is the whole of the first. Between them they use up the two shortest patterns available, and every other character in the standard is two marks or more.

That is why a chart matters more than it looks. Written with a period and a hyphen the two marks come out roughly the same width, which teaches the wrong rhythm from the first glance. Drawn to the ratio the standard sets, a dah is plainly three dits long, and the sound matches the picture.

How long a dash lasts

One unit is 1,200 milliseconds divided by the speed in words per minute (WPM), so a dah is three times that:

5 WPM: a dah lasts 720 milliseconds
10 WPM: 360 milliseconds
20 WPM: 180 milliseconds

Press Play above and move the speed control to hear the same mark at each of those lengths.

Building letters out of E and T

Because E and T are the shortest characters, they are also the building blocks of the next shortest ones. Take one dit and one dah and there are two letters to be had:

A is a dit then a dah
N is a dah then a dit

Double each mark and you get two more:

I is two dits
M is two dahs

Go to three marks of one kind and you reach S, three dits, and O, three dahs, which are the halves of the SOS distress signal. Between them, those six characters cover a good share of ordinary English text, which is part of why beginners are taught them first.

Sending a dash on a key

On a straight key a dah is nothing more than a longer press. The operator counts a steady beat, holds a dah for three counts and a dit for one, and leaves one count of silence between marks inside a letter and three counts between letters. Our SOS page sets out the same counting method for a flashlight, and the morse code translator will play any word you type so you can hear the beat before you try to send it.

Questions people ask next

What letter is a single dash in morse code?

T. It is one dah, and no other character in the international standard is a single dah.

How long is a dash in morse code?

Three units, where a dit is one. That is 180 milliseconds at 20 words per minute and 720 milliseconds at 5 WPM.

What is two dashes in morse code?

The letter M, sent as two dahs with a one-unit gap between them. Three dahs is O.

What is a dash and a dot in morse code?

The letter N. The other way round, a dot then a dash, is A.

Why is a dash drawn longer than a dot?

Because it sounds longer. ITU-R M.1677-1 fixes a dah at three units against a dit's one, so a chart that draws them the same length is showing the wrong signal.

Sources

Codes and timing follow Recommendation ITU-R M.1677-1 (10/2009), International Morse code (International Telecommunication Union, 2009).