Reading one is two questions: how many beats per measure, and what counts as a beat. 4/4 is four beats of a quarter note. 3/4 is three beats of a quarter note. 6/8 is six eighth notes, counted in two big beats.
What do the top and bottom numbers mean?
The bottom number names the note value being counted: 2 a half note, 4 a quarter, 8 an eighth, 16 a sixteenth (1 and 32 exist, but rarely). There is no note worth a third or a fifth, so a signature like 8/3 or 4/5 cannot exist; 3/16 and 9/16 are real, they simply count sixteenth notes. The top number says how many of those notes fill a measure. In simple time each one is a beat, so 3/4 is three quarter-note beats. When the top number is 6, 9 or 12 the time is compound, and the notes gather into big beats of three each: 6/8 moves in two beats, not six.
What a time signature really tells you is where the stress falls. 4/4 goes strong, weak, medium, weak; 3/4 goes strong, weak, weak. The same notes in the wrong meter come out as a different piece, because what a listener hears is the cycle of stresses, not the bar lines.
Which time signatures are common?
| Signature | Counted as | The beat is | You see it in |
|---|---|---|---|
| 4/4 | 4 beats | Quarter note | Most pop and study pieces; also written C |
| 3/4 | 3 beats | Quarter note | Waltzes, minuets |
| 2/4 | 2 beats | Quarter note | Marches, polkas |
| 2/2 (cut time, written ¢) | 2 beats | Half note | Marches, fast Baroque pieces, many hymns |
| 3/8 | 3 beats, or 1 at speed | Eighth note | Quick dances, scherzos |
| 4/8 | 4 beats | Eighth note | Light, quick pieces; rarer than 2/4 |
| 6/8 | 2 big beats of 3 | Dotted quarter note | Lullabies, barcarolles, jigs — see 6/8 time |
| 9/8 | 3 big beats of 3 | Dotted quarter note | Irish slip jigs, flowing slow pieces — see 6/8 time |
| 12/8 | 4 big beats of 3 | Dotted quarter note | Slow blues, ballads — see 6/8 time |
| 5/8 | 5 eighths: 3 + 2 or 2 + 3 | Eighth note | Balkan folk dances, modern pieces |
| 7/8 | 7 eighths: 2 + 2 + 3, 3 + 2 + 2 or 2 + 3 + 2 | Eighth note | Balkan folk music, modern pieces |
8/8 is eight eighth notes, usually grouped 3 + 3 + 2, which makes it feel lopsided where 4/4 feels even. 18/8 stretches compound time: six big beats, each three eighth notes long.
How do you count 5/8 and 7/8?
Count them in groups, not in single eighth notes. 5/8 is a group of three plus a group of two: ONE-two-three ONE-two when it is 3 + 2, and ONE-two ONE-two-three when it is 2 + 3. 7/8 follows the same rule with three groups — 2 + 2 + 3, 3 + 2 + 2 or 2 + 3 + 2. The score tells you which by how the eighth notes are beamed, and the first note of each group is the one to lean on.