Morse Code Timing

The Basics

The timing in Morse code is based around the length of one “dit” (or “dot” if you like). From the dit length we can derive the length of a “dah” (or “dash”) and the various pauses:

• Dit: 1 unit
• Dah: 3 units
• Intra-character space (the gap between dits and dahs within a character): 1 unit
• Inter-character space (the gap between the characters of a word): 3 units
• Word space (the gap between two words): 7 units

This timing is shown in the chart below where the message “WE GO” is visualised. You can hover over each element to see what they are, and zoom with the mouse wheel:

Words per Minute

The speed of Morse code is measured in the number of words per minute. This seems a tricky concept given that you can send more short words per minute than long ones. The work-around is to agree on using the word “PARIS” as the standard word, so if Morse is being sent at 20 words per minute (or “20 wpm”) then the word “PARIS” (or, more precisely “PARIS ” with a space on the end) could be sent 20 times in a minute.

The neat thing about “PARIS ” is that it’s a nice even 50 units long. It translates to “.--. .- .-. .. .../” so there are:

• 10 dits: 10 units;
• 4 dahs: 12 units;
• 9 intra-character spaces: 9 units;
• 4 inter-character spaces: 12 units;
• 1 word space: 7 units.

A grand total of $10 + 12 + 9 + 12 + 7 = 50$ units, as can be seen in the chart below:

Given this (and the fact that there are 60 seconds in a minute) we can therefore make a formula to find the length of a dit, $t_{dit}$ in seconds for a given wpm speed, $s_{wpm}$:

\begin{align} \text{words per minute} &= s_{wpm} \nonumber \\ \text{minutes per word} &= {1 \over s_{wpm}} \nonumber \\ \text{seconds per word} &= {60 \over s_{wpm}} \nonumber \\ \text{dits per word} &= 50 \nonumber \\ \text{seconds per dit} = t_{dit} &= {60 \over 50 s_{wpm}} \label{tdit} \end{align}

It’s clear that this makes sense: we know that for 1 wpm (i.e. $s_{wpm} = 1$) you must fit $50$ dits into a minute and the formula says $t_{dit} = 60/50$. As the speed ($s_{wpm}$) goes up, the length of $t_{dit}$ goes down (they are “inversely proportional”) which also makes sense.

The chart below shows the message “PARIS PARIS PARIS PARIS ” at a very slow 4 wpm, meaning that the message (of 4 words) takes a whole minute (or 60,000 ms) At 4 wpm the length of a dit is $60 / (50 \times 4) = 300\,\text{ms}$.

Further Reading

There are two other timing systems that are used in Morse code, especially when learning:

• Farnsworth Timing where the spaces between characters and words are stretched out. Useful for when learning instant character recognition.
• Wordsworth Timing where just the spaces between words are stretched out. Useful when more advanced and perhaps working on instant word recognition.

Both of these systems are explained in detail on their own pages.