Morse Code Timing: Dit Length, PARIS and WPM Explained

Every CW operator knows that a dah is longer than a dit, but surprisingly few can say exactly how much longer, how long the gaps should be, or what “20 words per minute” means in milliseconds. Morse code timing is the foundation of both sending and reading code. A keyer that is set well is easy to copy at any speed, while a hand-sent signal with uneven gaps is hard to read even at a modest speed. This guide explains the basic timing rules, the standard words used to measure speed, the simple formula that converts words per minute into dit length, and what happens when the spacing is stretched for learning. It is based on the standard description of International Morse code, and the numbers are easy to check with a calculator.

The Five Elements of International Morse

According to the Morse code reference article, International Morse code is built from five elements, all of which are multiples of one basic unit, the length of a dit. The unit is the clock of the whole system. If you know the length of one dit, you know every other length in the transmission.

• A dit (short mark) is one unit long.
• A dah (long mark) is three units long.
• The gap between the dits and dahs within one character is one unit of silence.
• The short gap between letters is three units of silence, the length of one dah.
• The medium gap between words is seven units of silence. It was formerly five units, so you may see that figure in older texts.

This is often called the 1-3-7 rule, although the full set of numbers is 1, 3, 1, 3 and 7. If you remember only one thing, remember that the spaces matter as much as the marks. A word gap is not simply a long pause; it is a precise length that tells the listener where one word ends and the next begins.

Why the Numbers Are Odd

There is a neat property hidden in these numbers. The dit and the dah are an odd number of units long (one or three), and the gaps that always follow them are also odd numbers (one, three or seven). Because of that, any character in International Morse comes out to an even number of units when both the marks and the spaces of the whole character are counted. The reference article points out that this gives ITU Morse a two-unit staccato beat, which helps telegraphers keep their sending rate steady. You can hear this beat in well-sent code: it has a rhythm that makes it easier to copy than uneven sending at the same speed.

What Is a Word per Minute?

Characters in Morse have different lengths, because they contain different numbers of dits and dahs. The letter E is a single dit, while the letter Q is dah dah dit dah. Consequently, words also have different lengths even when they have the same number of letters. To measure speed in a consistent way, a standard word is adopted. Two standards are in common use: PARIS and CODEX.

The word PARIS is the usual standard for the words-per-minute rate. When you add up the dits, the dahs and all the gaps, including the gaps between the letters and the gap that follows the word, PARIS takes 50 units. The word CODEX takes 60 units and gives a rate that is typical of five-letter code groups, or sequences of random letters. PARIS imitates a word rate that is typical of natural language, partly because the short codes for common letters such as E and T make normal text faster than random groups. If someone states a speed without naming the standard word, the figure can be ambiguous, though in amateur radio PARIS is almost always meant.

You can check the number yourself. P is dit dah dah dit, which is 1+1+3+1+3+1+1 = 11 units including the gaps inside the letter. A is dit dah, which is 1+1+3 = 5. R is dit dah dit, which is 1+1+3+1+1 = 7. I is dit dit, which is 3, and S is dit dit dit, which is 5. Add three units of gap after each of the first four letters, which is 12, and seven units of word gap at the end, which gives 11+5+7+3+5 = 31, plus 12 and 7 equals 50. That is why PARIS makes a convenient yardstick: it adds up to exactly 50 units.

The Formula: From WPM to Milliseconds

Because PARIS equals 50 units, the speed in words per minute tells you directly how many units fit into one minute: 50 times W units per minute for W words per minute. A minute has 60,000 milliseconds, so the length of one unit in milliseconds is 60,000 divided by (50 times W), which simplifies to 1,200 divided by W. The reference article gives the same relationship: T equals 1,200 divided by W, where T is the dit duration in milliseconds and W is the speed in words per minute. At 20 WPM, the dit is 60 milliseconds, and a dah is 180 milliseconds. With the CODEX standard, the dit length at 20 WPM would be 50 milliseconds instead, which shows why the standard word must be stated if you compare numbers.

The table below uses the PARIS standard and the 1,200 divided by W formula. The dah is three times the dit, the letter gap is three times the dit and the word gap is seven times the dit.

These figures are calculated from the formula, so they are theoretical values. Real keyers and operators vary a little, and the last decimal does not matter. What matters is the ratio between the elements.

Characters per Minute and Code Groups

You will sometimes see speeds given in characters per minute or in groups per minute instead of words per minute. A common convention, as the reference article notes in its description of testing standards, is that a word is five characters long, and a speed in words per minute is close to the PARIS standard while a speed in code groups per minute is close to the CODEX standard. The reference article also states that speeds measured with the PARIS and CODEX standard words may differ by up to 20 percent. This matters when you compare historical records or practice files, because the same number can mean different speeds depending on the standard used.

Speed Records and Human Limits

Human operators have pushed far beyond everyday speeds. According to the reference article, skilled operators can often understand code in their heads at rates over 40 WPM. In July 1939, at a contest in Asheville, North Carolina, Theodore Roosevelt McElroy, W1JYN, set a still-standing record for copying Morse at 75.2 WPM. The fastest speed ever sent with a straight key was reached in 1942 by Harry Turner, W9YZE, who sent 35 WPM in a demonstration at a US Army base. At those speeds, operators are hearing phrases and sentences rather than individual words. These records also depend on the standard word and the word gap in use at the time, so they are not exactly comparable with modern figures.

Farnsworth Spacing

When the spacing rules are stretched, the timing changes. In the Farnsworth method, each character is sent at the full target speed, with the normal relative timing of dits, dahs and the gaps within each character, but the gaps between characters and between words are made longer. For example, characters can be sent at a 13 WPM rate while the extra spacing lowers the overall text rate to 5 WPM. This gives learners time to think about the sound of each character without learning it as a slow, counted pattern. The spacing is shortened as skill grows. The method is named after Donald R. Farnsworth, W6TTB. We discuss the practical side, along with the Koch method, in our article on learning Morse code and building CW speed.

The key point for timing is that two speeds exist, a character speed and an overall speed. If you are practising with software, check which one the setting controls, since many programs have separate fields for them. A common mistake is to set a low character speed in order to learn slowly, which makes every character sound wrong and teaches the wrong patterns.

Weight, Ratio and a Good Fist

Real stations are not perfect clocks. Operators have individual characteristics, and the reference article describes this as their fist: some use slightly longer or shorter dahs or gaps, perhaps only for certain characters, and experienced operators can recognise individuals by it. A good operator who sends clearly and is easy to copy is said to have a good fist, while a sloppy sender has a poor fist. In practice, most keyers let you change the weight or the dit-to-dah ratio. The default of one to three is a safe starting point, since it is the standard definition. Small changes can make the code sound lighter or heavier, but large changes reduce readability and can make a signal sound strange. For paddle setup, see our guide to iambic keying modes.

On a straight key, you create the timing with your hand. The goal is a steady rhythm and the correct proportion between dits, dahs and gaps. Beginners usually make the gaps too short, which makes characters run together, and make dahs too short, which makes them sound like dits. An electronic keyer produces perfect timing but cannot compensate for a poor choice of speed. If you use a computer interface, the timing is also affected by the software and the hardware, and our guide to CW keying interfaces explains how a dedicated keyer improves it.

Timing and Break-In

Timing also affects how the radio behaves. At high speeds, the transmit and receive switching delay, which the radio needs to prevent clipped characters, becomes a larger share of each unit. At 30 WPM, a dit is only 40 milliseconds, so a transmitter that takes a long time to switch will shorten the first dit or the first characters. This is the reason that experienced operators pay attention to the delay settings on their radios. If you want to understand how full break-in works at speed, see our guide to full break-in CW and QSK, which explains how to set the delay.

Practical Tips

1. Choose a speed you can send perfectly. A slower, clean signal is easier to copy than a fast, sloppy one. Increase the speed only when you can maintain accuracy.
2. Listen to the gaps. If a word looks wrong when you copy it, the spacing may be the problem. Check that you are not leaving the character gap too short.
3. Use a keyer or software to learn. Practise with a program that sends perfect code, and compare your own sending by recording it.
4. Check the standard. When you compare speeds, make sure the same standard word was used, since PARIS and CODEX differ.
5. Do not shorten the word gap. A short word gap is a common cause of confusion, especially in contests. Our guide to Morse Runner shows how to practise at contest speeds.

The Bottom Line

Morse code timing is simple once you see the pattern. A dit is one unit, a dah is three, the gaps are one, three and seven, and the standard word PARIS contains 50 units, so the dit length in milliseconds is 1,200 divided by the speed in words per minute. Keep the ratios accurate, remember that stretching the gaps changes the overall speed without changing the character speed, state the standard word when you compare numbers, and listen for rhythm as much as for speed. Good timing is what makes code at any speed a pleasure to copy.

Frequently Asked Questions

How long is a dah compared with a dit?

A dah is three times as long as a dit. The gap inside a character is one unit, the gap between letters is three units and the gap between words is seven units.

How do I convert WPM to dit length?

Divide 1,200 by the speed in words per minute to get the dit length in milliseconds. For example, at 20 WPM, the dit is 60 milliseconds and the dah is 180 milliseconds.

Why is PARIS used to measure speed?

PARIS is a word that takes exactly 50 units, including the gaps, and it has a length similar to ordinary text. This makes it a convenient standard for calculating words per minute.

What is the difference between PARIS and CODEX?

PARIS takes 50 units and models normal language text, while CODEX takes 60 units and models five-letter random code groups. Speeds measured with the two can differ by up to 20 percent, so always check which one is used.

What is Farnsworth spacing?

Farnsworth spacing sends each character at full speed but lengthens the gaps between characters and words. This lets learners hear each character as a whole sound while the overall text speed stays low.

Why is the word gap seven units now?

The current International Morse standard uses seven units for the gap between words. It was formerly five units, so older books and historical records may use the earlier figure.