A loop should be a whole number of bars, and for most genres that means four or eight. Think in bars, not seconds: the seconds follow from the tempo, and the bars are what make the loop repeat cleanly. The formula is seconds = bars x beats per bar x 60 / BPM, so eight bars of 4/4 at 140 BPM is 13.714 seconds. The loop length calculator does the sum for any tempo, time signature and sample rate.
This guide covers how many bars to pick, the lengths each genre commonly lands on, why the exact sample count matters, how to bounce to it, and how the same tempo gives you delay times.
Think in bars, not seconds
A loop repeats by jumping from its end back to its start. That only sounds natural if the jump lands on a bar line, so the length has to be a whole number of bars at the project tempo. A loop that is 10.0 seconds long at 128 BPM is not a whole number of bars, and it will drift against anything laid over it.
The bar count is a musical choice. The seconds are a consequence, and a useful check on whether the choice suits where the loop is going:
- One or two bars is a riff or a drum pattern. Short enough that it needs the rest of the track to mean anything.
- Four bars is the usual unit for a chord progression or a melody: long enough to have a start, a middle and a turnaround.
- Eight bars gives a progression room to breathe and is the safest length for a loop that will be placed in someone else's session.
- Sixteen bars suits slow, sparse material, or a loop with a built-in change halfway.
What ColabLoop accepts
A loop on ColabLoop is one WAV, 10 to 60 seconds long and within the file size limit. That turns the bar count into a fit check. At a fast tempo, four bars is too short; at a slow one, sixteen bars may be too long. The sending loops guide has a table of 4, 8 and 16 bars at three tempos, and the calculator checks any combination you type, then suggests a bar count that fits when yours does not.
As a rule of thumb: eight bars lands between 10 and 60 seconds at almost every tempo producers actually use, which is part of why it is such a common choice. Four bars only clears 10 seconds below about 96 BPM in 4/4.
Common lengths by genre
These are conventions, not rules. They follow from where each genre's tempo sits (the BPM by genre guide has the ranges).
- Trap and drill sit at high tempos or half-time feels, so four bars can be under ten seconds. Eight bars is the usual choice for a loop that has to clear the minimum.
- Boom bap and lo-fi sit slower, so four bars often lasts long enough, and eight gives a melody time to resolve.
- Reggaeton and dancehall run on a repeating one-bar rhythm, so loops tend to be two, four or eight bars so that rhythm and harmony line up.
- R&B and slow melodic work often use four bars of chords played at a leisurely pace, and may need sixteen to feel like a phrase.
- Afrobeats loops commonly run four or eight bars, with the groove carried by the percussion pattern rather than by the chord length.
If you are unsure, eight bars is the one that rarely causes a problem.
Why the exact sample count matters
Audio files count in samples, and a seamless loop is exactly the right number of them. At 44.1 kHz, 8 bars of 4/4 at 140 BPM is 604,800 samples, a whole number, so a bounce can end on exactly that sample and the loop wraps without a seam.
Not every tempo is that tidy. At 48 kHz the same loop is 658,285.714 samples. A file cannot hold a fraction of a sample, so the end has to be rounded, here by about a third of a sample. That is far below what you can hear on a single pass, but it is not zero, and it shows why a long export at an awkward tempo can drift a hair against the grid.
What to do about it:
- Work at one sample rate from start to finish. A length that is exact at one rate is rarely exact at another, and converting adds its own rounding. The WAV sample rate and bit depth guide covers which to pick.
- Prefer a tempo that gives whole samples for the rate you work at, when the music does not care about 140 versus 139.5. The calculator shows whether the loop lands on a whole sample and how far off it is when it does not.
- Let the DAW place the end. Type the loop length in bars rather than dragging a selection, so the end sits on the bar line to the sample.
Odd time signatures change the bar, not the method. A 7/8 bar is seven eighth notes, which is 3.5 quarter notes, so at 120 BPM it lasts 1.75 seconds. Tempo in a DAW counts quarter notes whatever the signature, and the calculator follows that.
Bounce it to the right length
Knowing the length is half the job. The other half is getting a file that is exactly that long.
- Set the export range by bars. Start at bar 1, beat 1, and end on the bar line after the last bar. A selection that ends a sixteenth early is not eight bars.
- Check the length against the calculator. If the exported file is a few samples longer or shorter than the number it shows, the range was off. Most editors show a file's length in samples.
- Handle the tail. Reverb and delay ring past the last beat. If the export stops dead on the bar line the tail is chopped, so wrap it back onto the start. The seamless loops guide walks through two ways to do it.
- Match the project's sample rate. Do not let the export dialog convert.
- Loop the result. Play the file on repeat for a minute or two, on headphones, before anyone else hears it.
Match delay times to the tempo
The same tempo that sets the loop length sets the time of a delay or reverb. A delay set in milliseconds rather than synced to the host will not follow a tempo change, and some plugins only take milliseconds, so it helps to have the numbers.
The quarter note lasts 60,000 / BPM milliseconds. At 120 BPM:
- A quarter note is 500 ms.
- A dotted eighth is 375 ms, 1.5 times an eighth. This is the classic rhythmic delay.
- An eighth-note triplet is about 166.67 ms, two thirds of an eighth.
The calculator tabulates every note value from a whole note down to a thirty-second, straight, dotted and triplet, in milliseconds and in hertz. The hertz figure is the rate for a tempo-synced LFO or tremolo that should repeat once per note.
For reverb, two numbers matter. Pre-delay is the gap before the reverb starts, so the dry sound lands first; a small fraction of a beat is a common starting point. Decay is how long the wash lasts; tying it to the beat helps the tail clear before the next hit. Both are starting points to adjust by ear. For how this fits a loop you plan to hand to someone else, see should you mix loops.
Questions producers ask
How many bars should a loop be?
Four or eight for most genres. Eight is the safer choice when the loop has to be at least ten seconds, because four bars is short at fast tempos.
How long is a bar in seconds?
Beats per bar x 60 / BPM. In 4/4 at 120 BPM that is 4 x 60 / 120 = 2 seconds; at 140 BPM it is about 1.714 seconds.
Does a loop have to be a power of two in bars?
No, but one, two, four, eight and sixteen are what other producers expect and what drums and chord changes line up with. A three-bar or five-bar loop is fine if that is the music, and the calculator accepts any whole number of bars.
Does the sample rate change the length in seconds?
No. Seconds depend only on tempo, bars and time signature. The sample rate changes how many samples that is, and the file size.