Simple vs Compound Meter: How the Beat Divides

What is the difference between simple and compound meter?

The difference is how each beat splits: into 2 in simple meter, into 3 in compound meter. The number of beats per bar is a separate question. Both families can have two, three or four beats.

• Simple meter — the beat is a plain note (usually a quarter note) that divides into two eighth notes. Counted “1 & 2 &”.
• Compound meter — the beat is a dotted note (usually a dotted quarter) that divides into three eighth notes. Counted “1 la li 2 la li”.

Because a dotted quarter cannot be written as a single number, compound signatures show the division instead of the beat: 6/8 names six eighth notes, which form two dotted-quarter beats.

Duple, triple and quadruple: the classification table

Every regular meter has two labels: simple or compound, and duple, triple or quadruple. Duple means 2 beats per bar, triple means 3, quadruple means 4.

The most common entries are 2/4 (simple duple), 3/4 (simple triple), 4/4 (simple quadruple), 6/8 (compound duple), 9/8 (compound triple) and 12/8 (compound quadruple).

How to tell simple and compound meter apart

Look at the top number: 6, 9 or 12 means compound; 2, 3 or 4 means simple. Three checks settle the rest.

1. Read the top number. Top numbers of 6, 9 and 12 signal compound meter; 2, 3 and 4 signal simple meter.
2. Divide a compound top number by 3 to find the beats per bar: 6/8 has 2, 9/8 has 3, 12/8 has 4.
3. Listen to the subdivision. Tap the beat and hum the fastest steady notes: “1 & 2 &” is simple, “1 la li 2 la li” is compound.

The top-number rule fails at very slow tempos. A slow 6/8 is sometimes conducted in six, and a 3/8 bar at fast tempo is felt as one compound-like beat. Tempo decides which level the ear hears as the beat.

2/4 vs 6/8 side by side

2/4 and 6/8 both have two beats per bar; only the division differs. The grid below lines up one bar of each.

Playing a 2/4 march and a 6/8 march at the same felt beat shows the contrast: the first marches, the second skips. A composer who wants a triple division inside a simple meter writes triplets instead; a bar of 2/4 filled with eighth-note triplets sounds the same as a bar of 6/8.

Same felt beat, different BPM setting

A compound beat lasts 1.5 quarter notes, so compound meters need 1.5 times the quarter-note BPM to reach the same felt pulse. This site always counts quarter notes, so the entry differs even when the music feels equally fast.

The dotted-quarter lengths follow the ×1.5 rule in the dotted notes guide. Hear both families on the practice metronome by switching clicks per beat between Eighths and Triplets.

Where irregular meters fit

Irregular meters mix 2-part and 3-part beats in one bar, so they are neither simple nor compound. 5/4 groups quarter notes 3+2, and 7/8 groups eighth notes 2+2+3. The time signature overview charts all three families together.

Questions