Morse code timing: the 1, 3, 7 rule for dits, dahs and gaps
Morse code timing is built on one unit of time, the length of a dit. A dah is 3 units. The silence between the dits and dahs of one character is 1 unit, the silence between characters is 3 units, and the silence between words is 7 units. That is the whole rule, set out in the international standard (ITU-R M.1677-1), and every speed is the same pattern played faster or slower.
The rule is easy to say and easy to break, because most timing mistakes are not in the sounds at all. They are in the silences.
The five durations
Everything you send or hear is one of five lengths, all measured in units:
| Part | Length | At 20 WPM |
|---|---|---|
| Dit | 1 unit | 60 ms |
| Dah | 3 units | 180 ms |
| Gap inside a character | 1 unit | 60 ms |
| Gap between characters | 3 units | 180 ms |
| Gap between words | 7 units | 420 ms |
So the letter A, .-, is a dit, a one-unit gap and a dah: 5 units of sound and silence, heard as di-dah. The word AN, .- -., is A, then a three-unit gap, then N.
Notice that a dah and a gap between characters are the same length, 3 units. Your ear learns one as “sound” and the other as “silence”, and the proportions are what make Morse readable at any speed. Sent evenly, a slow operator and a fast one sound like the same rhythm at different tempos.
How long is a unit?
The unit depends on the speed, and speed in words per minute is measured with a standard word: PARIS. Sent with correct spacing, including the gap that ends it, PARIS is exactly 50 units long:
| Letter | Code | Units |
|---|---|---|
| P | .--. |
11 |
| A | .- |
5 |
| R | .-. |
7 |
| I | .. |
3 |
| S | ... |
5 |
| Four gaps between letters | 12 | |
| One gap after the word | 7 | |
| Total | 50 |
Count P to check the method: dit 1, gap 1, dah 3, gap 1, dah 3, gap 1, dit 1, which makes 11.
At 20 words per minute you send PARIS 20 times a minute, which is 1,000 units in 60 seconds, so one unit lasts 60 milliseconds. The general version is short enough to remember: a dit lasts 1200 divided by the WPM, in milliseconds.
| Speed | Dit (1 unit) | Dah (3 units) | Word gap (7 units) |
|---|---|---|---|
| 5 WPM | 240 ms | 720 ms | 1680 ms |
| 10 WPM | 120 ms | 360 ms | 840 ms |
| 15 WPM | 80 ms | 240 ms | 560 ms |
| 20 WPM | 60 ms | 180 ms | 420 ms |
| 30 WPM | 40 ms | 120 ms | 280 ms |
Real text has longer and shorter words than PARIS, so a minute of conversation will not land on exactly 20 words. The standard word only fixes the length of the unit; What WPM means in Morse code, and the PARIS standard goes further into it.
Why the gaps matter as much as the sounds
In Morse, a silence is information. Change its length and you change the message, and the receiver has no way to know you meant something else.
A letter gap that is too short merges letters. AN is .- -.. Close the three-unit gap down to one and the receiver hears .--., which is P. This is a common fault in hand-sent Morse, and it tends to get worse as you speed up, because a hurried hand squeezes the gaps first.
An element gap that is too long splits a letter. L is .-.., di-dah-di-dit. Pause after the dah and the receiver hears .- .., which is A followed by I.
A word gap that is too short runs words together. Seven units is a little more than twice a letter gap, and a word gap that shrinks to four or five units leaves the receiver guessing where one word ends.
The opposite errors are kinder. Gaps that are a little too long slow you down, but they rarely change the text. If you are unsure, err long while you learn, and tighten up once your rhythm is steady. Why your Morse letters run together, and how to fix spacing has drills for exactly this.
The one exception: prosigns
A prosign is two or more letters sent as a single character, with no letter gap between them. The best known is SOS, which is sent as ...---...: nine elements separated by one-unit gaps, one continuous signal. Sent as the separate letters ... --- ..., it is three letters, not the distress signal. The same goes for AR at the end of a message, .-.-., and SK at the end of a contact, ...-.-. More on sending it right in SOS in Morse code: how to send it correctly.
Farnsworth timing: stretching only the gaps
The 1, 3, 7 rule describes standard spacing, where the character speed and the overall speed are the same. Many learners use Farnsworth timing instead: each character is sent at full speed, but the gaps between characters and words are stretched, so the overall speed is slower.
The point is to learn each character as a fast, complete sound. A letter sent at 18 WPM has a rhythm you can recognize instantly, while the same letter at 5 WPM is a string of separate beeps that invites counting. With Farnsworth timing the dits, dahs and gaps inside each character keep their 1, 3, 1 proportions; only the gaps between characters and words grow, and in the usual way of working it out they grow together, keeping their 3 to 7 proportion. As your copying improves, you shrink the extra space until there is none left. Farnsworth spacing: what it is and when to drop it covers when to make that move.
If you practice on a Mac, Dot & Dash works this way out of the box: its machine starts at 18 WPM with Farnsworth spacing at 8 WPM, and Settings lets you set the speed from 5 to 40 WPM and the spacing separately. After each letter you key in a lesson, it draws your dits and dahs against the lengths they should have been and marks any that ran short or long, which makes uneven timing easy to spot.
Hearing and fixing your own timing
You cannot judge your own spacing while you send; you are too busy sending. A few ways to get an honest read:
- Let something else read it. A decoder only knows what your timing tells it. If it prints AN as P, or L as AI, the problem is a gap, not your memory of the code.
- Record yourself and listen the next day. Gaps that felt generous while sending often sound rushed on playback.
- Exaggerate the gaps for a week. Send with letter and word gaps that feel slightly too long. A rushed hand resets, and the gaps settle back to the right length as your rhythm steadies.
- Watch the dahs on a straight key. A tired or hurried hand tends to shorten its dahs, and the difference between a dit and a dah starts to blur. If your dahs sound clipped, slow down and lean on them.
- Know what a keyer does and does not do. With paddles and an electronic keyer, the dits, dahs and the gaps inside each character are timed for you. With a basic keyer, the gaps between letters and words are still yours.
Most timing problems fix themselves once you hear Morse as rhythm rather than as counted beeps. Counting units is a learning tool. At real speeds, a correctly spaced word has a shape you recognize, and a badly spaced one sounds wrong before you can say why.
Questions
Is the gap between words always seven units?
In standard timing, yes: 7 units, compared with 3 units between characters. With Farnsworth timing both gaps are stretched, and the usual way of working it out keeps them in the same 3 to 7 proportion.
How long is a dit at 20 WPM?
60 milliseconds, from 1200 divided by 20. At the same speed a dah lasts 180 ms, a gap between characters 180 ms, and a gap between words 420 ms.
Why is SOS sent without gaps between the letters?
SOS is a prosign: one character made of nine elements, sent as ...---... with only the one-unit gaps that belong inside a character. Sent with letter gaps, it is just the three letters S, O and S.
Do I need to count units while I send?
Only while you learn the proportions. Counting slows you down at higher speeds, so the aim is to hear and feel the rhythm, and to check it now and then with a recording or a decoder.