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My understanding of the bottom number in a time signature is that this is how many beats there are in a whole note. So if the bottom number is 4, a whole note gets 4 beats. If the bottom number is 2 a whole note gets 2 beats and if the tempo is 60bpm then it lasts 2 seconds instead of 4.

Is this right?

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    See my answer to a question about 6/8. "The bottom number is the beat" is an oversimplification that helps when starting to explain meter to beginners, but doesn't hold up for compound time. Sep 12, 2022 at 13:24
  • I've tried to ask almost this as well in this question. See if those answers answer your question!
    – EdvinW
    Sep 12, 2022 at 20:41

3 Answers 3

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"the bottom number in a time signature is ... how many beats there are in a whole note"

I wouldn't think of it as beats, necessarily; but certainly the denominator represents the note duration that fits 'that many' in a whole note.

In the US, of course, the maths is done for you: a quaver is an eighth note, so anything over 8 is in eighth notes; a minim is a half note, so anything over 2 is in half notes.

The problem with thinking in terms of 'beats in a whole note', is that this doesn't help you much with 3/4, or 5/4, or 9/8; unless your maths is very good.

(And 3/8 is often beated in one; 6/8 is usually beated in 2; 4/4 might be beated in 8 or 2, etc, etc.)

Also: metronome speeds are usually marked in terms of a note duration e.g. 'minim = 60', rather than just '60bpm'. So the 'calculation' you're making of the denominator in terms of a whole note doesn't really apply.

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  • What does the half note in 60 mean. 60 half notes in 60 seconds?
    – 7321
    Sep 13, 2022 at 14:16
  • @7321 That means "There are 60 half notes in a minute." There are 60 beats per minute, and those beats are half notes. Not quarters, nor eighths, nor anything else. Yes, 1 per second.
    – benwiggy
    Sep 13, 2022 at 15:06
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A time signature is similar to a fraction. In that the bottom number tells what the divisions are, while the top tells how many of them there are.

So, in 4/4 the bottom 4 tells each 'beat' is a crotchet (quarter note), while the top 4 tells there are 4 of them in each bar. Similarly with 3/4. 3 crotchets per bar. 5/4 tells 5 crotchets per bar, unsurprisingly.

6/8 tells there are 6 quavers in each bar, which is the same as 3/4 mathematically, but actually doesn't reveal that the rhythm of the bar is quite different, though. That's often where the confusion between 3/4 and 6/8 is found. 7/8 unsurprisingly tells 7 quavers (eighth notes) in each bar - but again, a little like 6/8, doesn't give a clue in itself how those quavers are grouped, rhythm wise.

The concept of a 'whole note' :- a whole note is called a semibreve, which is made up of two minims,(1/2 notes) or 4 crotchets,(1/4 notes). It is the hollow egg-shaped note, with no stem. It doesn't have too much bearing on things - except that it is the 'whole' that is divided, as explained in this paragraph. A whole note will fit into one bar of 4/4, but not into a whole bar of 3/4. Hence 3/4 gets called 'three-quarter time' quite often. That, and after all, it looks exactly like the fraction - 3/4!

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    Thanks for addressing the OP's core confusion about "whole note"! Sep 12, 2022 at 13:25
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Yes, that's correct. Just keep in mind that a whole note need not fit in a single measure. For example, in 6/8 time, a whole note gets eight beats, but each measure only has 6. Similarly, for 3/4 time, a whole note gets four beats, but each measure contains only three.

See also I don't understand the bottom number in a time signature, which explains the same concept in a different way.

There is also a concept of "irrational" time signatures, such as 4/3 or 6/10. The rule holds here as well. In 4/3, a whole tone would receive 3 beats, and a measure would contain four 1/3-beats. ("Irrational" in this sense is distinct from the mathematical idea of irrational numbers.)

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  • Wha??? Was the question edited after you answered? If the time signature is 6/8 then there are not 8 beats in a whole note. There aren’t even two beats. A whole note always equals four quarter notes. A whole rest may be used as a measure long rest even when the measure is not four quarters long. A measure of 6/8 contains two beats, not six. Sep 12, 2022 at 22:16
  • @ToddWilcox In 6/8 time, it is frequently taught that the eighth note get the beat. There are eight eighth notes in a whole note; therefore, eighth beats.
    – Aaron
    Sep 12, 2022 at 22:54
  • Seems like it’s frequently taught wrong Sep 13, 2022 at 0:22
  • @ToddWilcox That's been the standard for every teacher I've had, including conservatory. I'd never heard it taught as 2 beats per measure until I got here. It was always "six beats the the measure; the eighth note gets one beat." It's not wrong; just different than what you're used to.
    – Aaron
    Sep 13, 2022 at 1:15
  • I was literally talking with a professor a few hours ago about 12/8 and 9/8 time and he definitely would have said I was wrong if I counted those measure with 12 or 9 beats respectively. We had a whole discussion about how I should be thinking of those time signatures. I can’t imagine how you could have conservatory teachers suggesting you count 6/8 as "1 2 3 4 5 6" instead of "1 & uh 2 & uh" (or equivalent). How could you follow a conductor counting 6/8 in six? You couldn’t even play drums for Chevelle if you played 6 beats in 6/8. Sep 13, 2022 at 2:54

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