S in Morse code

S is dot dot dot in International Morse code, said “di-di-dit”. It has 3 elements and lasts 5 units, which is 300 ms at 20 WPM.

S on a timing ruler

Dots last one unit, dashes three, and the gaps inside the letter one unit each. The numbers under the ruler are the length of each part.

How to remember S

S is I with one more dot on the end.
Add a dot and you get H or a dash and you get V.
... reads the same forwards and backwards.
Say it out loud as “di-di-dit”. Learning the rhythm, not counting dots and dashes, is what lets you recognise it at speed.
S is character 6 of 41 in the Koch learning order, followed by N. Practise it in the Koch trainer.

Letters that sound like S

These are the letters most often copied by mistake for S, and why.

Can you hear the difference?

Listen, then pick the one you heard.

S on the air

SOS (...---...) is sent as one continuous signal, not as three separate letters. The S's frame it.
SK (...-.-) is the ITU end-of-work signal, sent to close a contact.

S at a glance

Morse code: ...
Sounds like: di-di-dit
Length: 5 units
At 20 WPM: 300 ms
NATO word: Sierra
Frequency in English: 6.3% (7th of 26)

Sources: codes from ITU-R M.1677-1, the International Morse code standard; English letter frequencies from Robert Lewand’s analysis; American Morse from the historical US telegraph code.

Hear S at your speed