BEATTIMING
Sample tempo finder

Loop BPM and time-stretch calculator

Find a loop's quarter-note BPM from its duration, bar count and time signature, then calculate the exact speed change and new duration for a target tempo.

Detected quarter-note tempo120.000 BPMPossible half-time 60.000 BPM · double-time 240.000 BPM
New duration at 128 BPM0:07.500
Tempo change+6.667%
Playback speed ratio1.066667×
Duration change−6.250%

The result uses quarter-note BPM for a DAW tempo grid. Tempo change and resulting-duration percentage are labeled separately because “stretch percentage” is ambiguous between apps.

Formula

How to find BPM from a loop's length

Convert the loop's notated length into quarter-note beats, multiply by 60 and divide by its duration in seconds. Once the original BPM is known, the target-to-original BPM ratio gives the required playback-speed or time-stretch change.

BPM = bars × meter numerator × (4 ÷ denominator) × 60 ÷ duration

  1. 01

    Trim leading silence and trailing audio before measuring the duration.

  2. 02

    Enter the loop length in bars (quarter-bar increments are supported) and choose its time signature.

  3. 03

    Compare the detected, half-time and double-time values with the style and feel of the loop.

Worked example

Example: an eight-second four-bar loop

A four-bar loop in 4/4 contains 16 beats. If it lasts exactly eight seconds, its tempo is 120 BPM. To fit 128 BPM, increase playback speed by 6.667%, producing a new duration of 7.5 seconds.

Good to know

Assumptions and limits

  • The loop starts and ends exactly on the entered musical-bar or bar-subdivision boundaries.
  • The BPM remains constant through the entire loop.
  • The main result is quarter-note BPM; compound meters also show the dotted-quarter pulse separately.
  • Half-time and double-time results describe alternate ways to count the same pulse, not different audio durations.
  • Clock displays round to the nearest millisecond; tempo and percentage calculations use unrounded values.
Quick answers

Frequently asked questions

How do I calculate BPM from seconds?

Convert the loop's bar count and time signature to quarter-note beats, multiply by 60, then divide by its exact duration in seconds.

Why is the detected BPM half or double what I expected?

Tempo can be counted at different pulse levels. A loop analyzed as 70 BPM may also be described as 140 BPM without changing its duration.

Does time-stretching change pitch?

Pitch-preserving time stretch changes duration without changing pitch. Resampling or varispeed changes tempo and pitch together.