A dotted quarter note lasts 3/8 of a whole note: more than a quarter note and less than a half note. It is a common calculation when reading a measure, and it uses the same fractions you use to add. The whole note is the unit. How many seconds it lasts depends on the tempo, but the ratios between note values never change.
Each note value is half the one before
| Note | Fraction of a whole note | How many fit in a whole note |
|---|---|---|
| Whole note | 1 | 1 |
| Half note | 1/2 | 2 |
| Quarter note | 1/4 | 4 |
| Eighth note | 1/8 | 8 |
| Sixteenth note | 1/16 | 16 |
| Thirty-second note | 1/32 | 32 |
| Sixty-fourth note | 1/64 | 64 |
The denominators are powers of 2 because each note value comes from splitting the previous one in two. That is why a quarter note equals two eighth notes or four sixteenth notes, which are equivalent fractions: you get them by multiplying the numerator and denominator by the same number. The English Wikipedia article Note value lists the same values as fractional powers of two, with the whole note as the unit (accessed October 17, 2026).
Calculating a dotted note
A dot to the right of the note head adds half of the note’s value. The same source describes it as making the note one and a half times its original length, which is multiplying by 3/2.
Worked example: filling a 3/4 measure
A 3/4 measure holds a dotted quarter note, an eighth note, and a quarter note. Is it full?
- Value of the dotted quarter note. 1/4 + 1/8 = 2/8 + 1/8 = 3/8.
- Add the eighth note. 3/8 + 1/8 = 1/2.
- Add the quarter note. 1/2 + 1/4 = 3/4.
Result: the total matches the time signature, so the measure is full.
Check: in eighths, 3 + 1 + 2 = 6, and six eighths is what the time signature calls for.
A double dot adds half the value and then half of that half. On an eighth note it gives 1/8 + 1/16 + 1/32 = 7/32. To find what is missing in an incomplete measure, subtract the written length from the length the measure holds. To add notes of different values, adding fractions brings them to a common denominator, and comparing fractions tells you which of two durations is longer.
6/8 and 3/4 last the same and sound different
As fractions they are equal: two dotted quarter notes add up to 3/8 + 3/8, the same length as three quarter notes. What changes is the grouping and where the beats fall.
| Time signature | Beats | Each beat | Counted |
|---|---|---|---|
| 3/4 | 3 | a quarter note, divided into 2 eighth notes | 1-2-3 |
| 6/8 | 2 | a dotted quarter note, divided into 3 eighth notes | 1-2-3, 4-5-6 |
That is why a time signature is never simplified. The English Wikipedia article Time signature explains that in a simple meter the top number counts the notes of the type named by the bottom number, while in a compound meter the beat divides into three, so 6/8 is felt as two beats of a dotted quarter note each (accessed October 17, 2026). If you swap one for the other, the accents change even though the total is the same.
The triplet breaks the rule of powers of 2
An eighth-note triplet is three eighth notes in the time of two. Two eighth notes last 1/4, so each note of the triplet lasts 1/4 ÷ 3 = 1/12 of a whole note. The 12 is not a power of 2, which is why the triplet has no note value of its own and is marked with a 3 over the group. Three of them add up to 3/12, a quarter note.
Practice with note values and measures
Practice
- How long is a dotted eighth note?
- A 2/4 measure holds a dotted quarter note and a sixteenth note. Which note is missing to fill it?
- How many sixteenth notes fit in a 6/8 measure?
Show the answers
- 1/8 + 1/16 = 3/16 of a whole note.
- 3/8 + 1/16 = 7/16, and 1/2 − 7/16 = 1/16: another sixteenth note is missing.
- 6/8 = 12/16, so 12 fit.
If you want to review the idea of a fraction before adding note values, the guide what are fractions builds it from scratch, and the fraction calculator solves any sum of durations. More reading like this is on the blog.
Sources
- English Wikipedia, article “Note value,” accessed October 17, 2026.
- English Wikipedia, article “Time signature,” accessed October 17, 2026.