Morse code timing comes down to four ratios defined in ITU-R Recommendation M.1677-1: a dash lasts three dot-lengths, the silence between elements in the same letter lasts one dot-length, the silence between letters lasts three dot-lengths, and the silence between words lasts seven dot-lengths. Everything else scales from those ratios.
The Four Timing Rules
The ITU standard specifies these rules in Section 2 of Annex 1:
| Element | Duration (in dot units) |
|---|---|
| Dot (dit) | 1 |
| Dash (dah) | 3 |
| Gap between elements within a letter | 1 |
| Gap between letters in a word | 3 |
| Gap between words | 7 |
These ratios hold at any speed. At 20 words per minute, one dot lasts 60 milliseconds (ms). At 10 WPM it lasts 120 ms. The sound of the code changes with speed, which is why learning at too slow a speed creates habits that don’t transfer.
What Is a “Word”?
Morse code speed is measured in words per minute (WPM) using the standard word PARIS. PARIS was chosen because it contains a mix of short and long characters and sums to exactly 50 unit-lengths including inter-character and inter-word gaps:
- P: .–. = 1+1+3+1+3+1+1+3 = 14 units (including trailing letter gap)
- A: .- = 1+1+3+3 = 8 units
- R: .-. = 1+1+3+1+1+3 = 10 units
- I: .. = 1+1+1+3 = 6 units
- S: … = 1+1+1+1+1+7 = 12 units (trailing word gap)
- Total: 14+8+10+6+12 = 50 units
At 20 WPM the code transmits 20 × 50 = 1,000 units per minute, so one unit = 60 ms. This is the standard formula.
Calculating Dot Length from WPM
dot_length_ms = 1200 / WPM| Speed (WPM) | Dot length | Dash length | Letter gap | Word gap |
|---|---|---|---|---|
| 5 | 240 ms | 720 ms | 720 ms | 1,680 ms |
| 10 | 120 ms | 360 ms | 360 ms | 840 ms |
| 13 | 92 ms | 276 ms | 276 ms | 646 ms |
| 20 | 60 ms | 180 ms | 180 ms | 420 ms |
| 25 | 48 ms | 144 ms | 144 ms | 336 ms |
A Worked Example: Sending “SOS”
SOS is the international distress signal, sent as a single prosign (· · · — — — · · ·) without normal letter gaps:
- S: dot gap dot gap dot = 1+1+1+1+1 = 5 units
- Then a single element gap of 1 unit (not the 3-unit letter gap, because SOS is one continuous signal)
- O: dash gap dash gap dash = 3+1+3+1+3 = 11 units
- Then 1 unit gap
- S: 1+1+1+1+1 = 5 units
- Total signal: 5+1+11+1+5 = 23 units
At 13 WPM (92 ms per unit), the full SOS prosign takes about 2.1 seconds. When sent with normal letter gaps (3 units between S–O and O–S), it takes a bit longer — 5+3+11+3+5 = 27 units = 2.5 seconds.
Farnsworth Timing
Farnsworth timing is a training technique where characters are sent at a faster internal rate — say 18 WPM within each character — but the gaps between letters and words are stretched to produce a slower effective copy rate. For example, at 18/9 Farnsworth (18 WPM character speed, 9 WPM effective speed):
- Dot length at 18 WPM: 67 ms
- But inter-letter gap is expanded so the overall rate feels like 9 WPM to the copyist
This lets learners hear each character at real speed while having time to write it down. As accuracy improves, the gaps shrink.
Why Ratios Matter, Not Absolute Times
Because all elements scale together, the code sounds proportionally the same at any speed. A skilled operator copying at 25 WPM hears a pattern that is rhythmically identical to the same character at 5 WPM — just faster. This is why experienced operators can decode Morse without consciously counting dots and dashes.
See how to learn Morse code for practice methods that take advantage of these timing ratios, and Morse code with light and sound for how to apply these timings when signaling visually. The Morse code translator shows you the correct dot-dash output for any text you enter.