What BPM means in music
BPM is beats per minute: how many beats pass in a minute. It is the one number that sets how fast a piece of music moves. At 60 BPM a beat lasts a second. At 120 it lasts half a second.
What the number means
Tap a foot to a song. Each tap is a beat. Count the taps in one minute and that is the tempo in BPM. Wikipedia puts it plainly: "A tempo of 60 beats per minute signifies one beat per second, while a tempo of 120 beats per minute is twice as rapid, signifying two beats every second."
The number became common in the first half of the 19th century, after Johann Maelzel's metronome gave musicians a machine that ticked at a set rate. Before it, tempo was written as a word: adagio, andante, allegro.
A beat, a bar and a step
Most music is counted in bars of four beats. A drum machine cuts each beat into four more, so a bar is sixteen steps, each a sixteenth note. The tempo sets the length of all three.
A beat lasts 60 seconds divided by the BPM. A bar of four lasts four of those. A step lasts a quarter of one.
| BPM | A beat | A bar | A step |
|---|---|---|---|
| 60 | 1,000 ms | 4.00 s | 250 ms |
| 70 | 857 ms | 3.43 s | 214 ms |
| 90 | 667 ms | 2.67 s | 167 ms |
| 120 | 500 ms | 2.00 s | 125 ms |
| 140 | 429 ms | 1.71 s | 107 ms |
| 170 | 353 ms | 1.41 s | 88 ms |
The figure shows why tempo is felt so strongly. A bar at 170 BPM is over before a bar at 70 is half done.
Half time
The BPM on the dial is not always the tempo a listener feels. Trap is set at about 140 BPM, and its clap falls once a bar, on beat three. A listener nods to that clap, so the beat is felt at 70. The hats still run at the speed of 140. This is called half time.
The bar below is set at 140. Press PLAY and count with the clap.
| Kick | 1, 13 |
|---|---|
| Clap | 9 Once a bar, on beat three. |
| Hat | 1, 3, 5, 7, 8, 9, 11, 13, 15 |
| Tempo | 140 BPM Felt at 70. |
Which tempo for which music
A genre is a tempo as much as a pattern. House sits at 120 to 130 BPM, boom bap at 85 to 95, drum and bass at 160 to 180. Tempo by genre draws twelve of them on one scale, each with its sources.
On Beep Boop
TEMPO is the knob at the left of the bottom row. It runs from 40 to 300 BPM, and the window shows the number in orange figures as it turns.
Inside, the tempo is a count of samples. Beep Boop makes 48,000 samples of sound a second on an iPhone, so at 120 BPM a step is 6,000 samples long. Each step starts on the sample the count puts it on, which is why the beat does not drift. Swing is counted the same way.
Sources
- The definition, the metronome and the Italian words: Tempo, Wikipedia.
- Trap at 140, counted at 70: Trap music, Wikipedia. The genre ranges: Tempo by genre, with its own sources.
- The knob's range and the sample counts: Beep Boop's engine, which measured 48,000 samples a second on an iPhone 14 Pro Max and places every step by counting them.
More sheets
- What swing is in musicThe late step, measured in milliseconds.
- How to make a beatFour moves on sixteen steps.
- What syncopation isThe weight off the beat, on sixteen steps.
- Ghost notes and accents on drumsLoud and quiet strokes in one bar.
- PatternsDrum patterns drawn on sixteen steps.
- Tempo by genreBPM for twelve genres, on one scale.