Where the Number 1200 Comes From in Morse Timing

Every speed in Morse code traces back to a single number: 1200. Divide it by the words-per-minute you want and you get the length of one dit in milliseconds. At 20 WPM a dit is 60 ms. At 5 WPM it is 240 ms. Nothing else about the timing is free to vary.

That constant is not arbitrary, and understanding where it comes from explains most of what beginners find confusing about code speed.

The word that defines the speed

Morse speed is measured against a reference word, and the reference word is PARIS followed by a word space. Sent at exactly one word per minute, PARIS takes sixty seconds. Sent at 20 WPM, it takes three.

PARIS was chosen because it happens to total exactly 50 dit-time units — near the average for ordinary English text, and a round number to divide by. Sixty thousand milliseconds in a minute, divided by fifty units, gives 1200 milliseconds per unit at one word per minute. Divide by the WPM and you have the dit length. That is the whole derivation.

Where the fifty units go

Counting PARIS unit by unit is worth doing once, because it explains why Farnsworth timing works the way it does.

A dit is 1 unit. A dah is 3. The gap between elements inside a letter is 1. The gap between letters is 3, and the gap between words is 7. Add up everything inside the letters of PARIS — the dits, the dahs, and the gaps between their elements — and you get 31 units. Add up the gaps between letters and the word space at the end and you get 19. Thirty-one plus nineteen is fifty.

That split is the key. The 31 units are the letters themselves; the 19 units are silence.

What this means in practice

Run any speed through the WPM and Farnsworth calculator and every figure it returns is a multiple of that one dit length:

• dit = 1200 ÷ WPM
• dah = 3 dits
• gap inside a letter = 1 dit
• gap between letters = 3 dits
• gap between words = 7 dits

At 20 WPM that is a 60 ms dit, a 180 ms dah, and a 420 ms word space. At 13 WPM — the old US licence requirement — the dit stretches to 92.31 ms and everything else stretches with it.

Why "words per minute" is not literally words

A common source of confusion: 20 WPM does not mean you will copy twenty ordinary English words in a minute. It means you will copy the equivalent of twenty PARIS-lengths.

Real words vary. Short common words run under fifty units; long or unusual ones run well over. Text with numbers in it is slower still, since every digit is five elements. The PARIS standard exists precisely so that two operators quoting a speed mean the same thing, whatever they happen to be sending.

The other standard word

You will occasionally see speeds quoted against CODEX instead, which totals 60 units rather than 50. It is more representative of text containing numbers, and it is common in commercial and military contexts.

A speed quoted in CODEX words per minute is slower than the same number quoted in PARIS words per minute, by the ratio 60:50. If a figure ever seems 20% off from what you expected, this is usually why. Amateur radio uses PARIS almost universally, which is the convention these tools follow.