# What reverb time fits my tempo?

Works out reverb pre-delay and decay times in milliseconds that fit a song’s tempo in BPM, for a bar, half note, quarter note or eighth note, straight, dotted or triplet.

- Page: https://www.acalculator.org/everyday-life/reverb-calculator
- JSON spec: https://www.acalculator.org/everyday-life/reverb-calculator.json
- Version: 053645e201b0

## Default answer

Example with the default inputs (Tempo (BPM) 120, Reverb length 1/2 note (room), Note feel Straight, Pre-delay 1/64 note): At 120 BPM, set a pre-delay of 31.25 ms and a decay of 968.75 ms.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| bpm | Tempo (BPM) | The song’s tempo in beats per minute. |
| len | Reverb length | How long the whole reverb should last: a bar for a hall, shorter for a room. |
| feel | Note feel | Straight, dotted (1.5 times as long) or triplet (2/3 as long). |
| pre | Pre-delay | The gap before the reverb starts, as a short note. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| decay | Decay time | The length less the pre-delay. |
| predelay | Pre-delay | One beat × the pre-delay note’s part of a beat. |
| total | Total reverb time | One beat × beats in the length (× 1.5 dotted, × 2/3 triplet). |
| beat | One beat | 60,000 ÷ BPM ms, a quarter note. |
| table | Decay for each length | The decay time for a bar, a 1/2, a 1/4 and a 1/8 note, with the same feel and pre-delay. |

## Method

Beat = 60,000 ÷ BPM ms; total = beat × beats in the length × feel (1, 1.5 dotted, 2/3 triplet); pre-delay = beat × 4 ÷ N for a 1/N note; decay = total − pre-delay.

## Assumptions

- The beat is a quarter note and a bar is four beats, as in 4/4 time.
- Pre-delay plus decay fill the chosen musical length, so the tail ends on the beat.
- The pre-delay keeps its straight length; the feel changes only the reverb length.

## Worked examples

1. bpm = 120, len = 2, feel = straight, pre = 64 gives beat = 0.5, predelay = 0.03125, total = 1, decay = 0.96875. Source: TuneLens, Reverb Time Calculator (pre-delay about a 1/64 note; decay = the musical length less the pre-delay; a bar of 4/4 is 240,000 ÷ BPM ms), https://tunelens.com/reverb-time-calculator.html (retrieved 2026-10-03); SI Brochure (BIPM, 9th edition, 2019), Table 8: 1 min = 60 s.
2. bpm = 90, len = 4, feel = dotted, pre = 128 gives beat = 0.666667, total = 4, predelay = 0.020833, decay = 3.979167. Source: TuneLens, Reverb Time Calculator (pre-delay about a 1/64 note; decay = the musical length less the pre-delay; a bar of 4/4 is 240,000 ÷ BPM ms), https://tunelens.com/reverb-time-calculator.html (retrieved 2026-10-03); SI Brochure (BIPM, 9th edition, 2019), Table 8: 1 min = 60 s.
3. bpm = 128, len = 1, feel = triplet, pre = none gives total = 0.3125, decay = 0.3125, predelay = 0. Source: SI Brochure (BIPM, 9th edition, 2019), Table 8: 1 min = 60 s.

## FAQ

### How do I time reverb to the tempo?

Work out one beat in milliseconds, 60,000 ÷ BPM, and pick a musical length for the whole reverb, such as a half note (2 beats). Take off a short pre-delay and set the rest as the decay. At 120 BPM a half note is 1,000 ms; with a 31.25 ms pre-delay, the decay is 968.75 ms.

### What is reverb pre-delay?

The gap between the dry sound and the start of the reverb. A short pre-delay, often about a 1/64 note, keeps the start of each note clear before the reverb fills in behind it.

### Which reverb length should I pick?

A bar suits a large hall or a slow ballad, a half note a room, and a quarter or eighth note a tight ambience on drums or fast parts. Try the length that leaves space before the next hit.

### What do dotted and triplet mean here?

A dotted length is 1.5 times the straight one; a triplet length is 2/3 of it. Use them when the song swings or the part plays in triplets.

### Is the decay time the same as RT60?

Many plugins set decay as the time for the reverb to fade by 60 dB (RT60), others to silence. Either way, a tempo-based value is a starting point; trust your ears.

## Sources

- TuneLens, Reverb Time Calculator (a pre-delay of about a 1/64 note; the decay fills the rest of the musical length; a bar of 4/4 lasts 240,000 ÷ BPM ms). https://tunelens.com/reverb-time-calculator.html (retrieved 2026-10-03)
- BIPM, The International System of Units (SI Brochure), 9th edition, 2019, Table 8 (1 min = 60 s). https://www.bipm.org/en/publications/si-brochure (retrieved 2026-10-03)