Online Metronome
Set the BPM with the slider or with tap tempo, choose the beats per measure, and play in time: the downbeat is accented and the indicator pulses on every click.
100 BPM
Why the downbeat is accented
The higher-pitched click marks the start of each measure and helps you "feel" the meter of the song: 4 beats gives you the classic 4/4 of pop and rock, 3 gives you waltz time, and 6 fits songs in 6/8. If you just want a steady click with no measure reference, pick 1, every beat will sound the same. The most effective way to clean up a tricky passage is to practice it slowly (even 60–70 BPM) and raise the tempo 5 BPM at a time.
How to use tap tempo
Don't know a song's BPM? Press the "Tap tempo" button along with the music, at least 4–5 times in a row: the metronome averages the intervals between your taps and sets the matching tempo. If you lose the beat, just stop for a couple of seconds and start tapping again, the count resets automatically.
Why playing with a metronome is hard
It is not a lack of rhythm: it is that the metronome does not adapt. Playing alone you slow down imperceptibly in the hard passages and speed up in the easy ones, and without an external reference you never notice. The click makes it obvious, and the first sensation is of always being late.
The remedy is not more concentration but a lower tempo: choose a speed at which the passage comes out clean every time, and go up two or four BPM at a time. It is the only method that works, and it holds for any instrument. Playing fast and dirty teaches you to play dirty.
The missing beat is the one that teaches
The most effective way to use a metronome is not to have it click on every beat, but to take it away. Set to half tempo, the click lands only on the first and third beat and you have to hold the rest yourself: it is far harder, and anyone who can do it has genuinely internalised the pulse.
The next step is putting it on the weak beats, that is the second and fourth: that is the feel of swing and backbeat, and it is how studio musicians work. At first the ear gets lost and flips the perception, and that moment of disorientation is precisely the exercise.
Where the number comes from
The mechanical metronome dates from 1815, patented by Maelzel, which is why scores still read M.M., «Maelzel's metronome», before the number. Beethoven was the first great composer to write tempos as figures, and his values are still argued over because they seem faster than his works are played today.
The Italian tempo names remain the common language: largo around forty to sixty beats, andante between seventy and a hundred, allegro between a hundred and twenty and a hundred and sixty, presto above. They are indicative bands, not definitions: between two editions of the same symphony the number changes, the name does not.
When the click is not enough
If you are recording, the metronome should be replaced by the grid of the software, because what matters is that the tracks line up with each other. And if you are playing music that breathes, that is almost all classical music and much acoustic music, the metronome belongs to the practice room and not to the performance: there the tempo is held by the phrase, not by the click.
Finally there is a use that is not musical at all: the metronome is a training tool. Running, rowing, skipping or doing exercises at a steady rate works better with an external reference, and the effort spreads more evenly.
Nearby tools
The tempo of a track is found with BPM tap counter, and effect milliseconds with BPM to milliseconds. To practise there are Musical scales and Chord progressions, and for timed intervals Interval timer.