Reverb Decay Calculator
Decay — also called the tail or the reverb length — is whatever is left of a musical total once the pre-delay is subtracted. Set it this way and the wash ends on the grid, every time.
| Pre-delay note | Pre-delay | Decay |
|---|---|---|
| 1/32 | 62.5 ms | 937.5 ms |
| 1/64 | 31.25 ms | 968.75 ms |
| 1/128 | 15.63 ms | 984.38 ms |
| 1/256 | 7.81 ms | 992.19 ms |
| 1/512 | 3.91 ms | 996.09 ms |
Decay is always total − pre-delay — change either number and the tail still ends on the grid.
The method: choose the total first, then subtract the gap
Most producers set decay by twisting a knob until the tail feels about right, then wonder why the mix clouds up at the chorus. This tool reverses the order. You first decide where the reverb must be finished — the next bar line, the next chord, the next drum hit — and express that endpoint as a total time taken from a note value. The decay is then not a guess at all; it is the remainder after the pre-delay.
total (ms) = quarter note × note fraction
decay = total − pre-delay
Decay time, reverb tail and reverb length are three names for this same remainder, which is why searches for any of them land on this one tool. The distinction that matters is total versus decay: the total is measured from the moment the source plays, while the decay is measured from the moment the tail actually starts, after the gap. Plugins differ in which of the two their main knob controls, so knowing both numbers — which is what this page gives you — lets you translate the setting to any unit.
The totals used here are the same sizes as the combined console on the home reverb and delay calculator, so a decay worked out on this page will match the console table at the same tempo exactly.
Reference table: decay after a 1/64 pre-delay at 120 BPM
At 120 BPM a 1/64 pre-delay is 31.25 ms. The table subtracts that fixed gap from a ladder of totals, showing how little the gap costs a long tail and how much of a short total it consumes — a 1/16-note total loses a quarter of its length to the gap, while a 2-bar total barely notices it.
| Total length | Total (ms) | Pre-delay (ms) | Decay (ms) |
|---|---|---|---|
| 2 bars | 4000 | 31.25 | 3968.75 |
| 1 bar | 2000 | 31.25 | 1968.75 |
| 1/2 note | 1000 | 31.25 | 968.75 |
| 1/4 note | 500 | 31.25 | 468.75 |
| 1/8 note | 250 | 31.25 | 218.75 |
| 1/16 note | 125 | 31.25 | 93.75 |
If your gap is a different note value, the dedicated pre-delay calculator for sizing the gap itself lists every small note value at 90, 120 and 150 BPM, ready to subtract from any total in this table.
Fitting decay into the space the arrangement leaves
Measure the gap before the next event
The governing question is not how big a space you want — it is when the next important sound arrives. On a backbeat snare in 4/4, the next hit comes 2 quarter notes later, so at 120 BPM the entire reverb, gap included, has 1000 ms to live. A ballad vocal over half-time drums may have a full bar or two. Count that interval first, pick the largest note-value total that fits inside it, and the decay follows automatically. The backbeat case is automated in full on the snare calculator built around the next-hit rule, including separate fractions for kick, toms and overheads.
Typical lengths by genre feel
Genres differ mostly in how much empty grid they leave, which is why their characteristic tails differ. Tight funk, modern pop and fast punk live at short totals — a 1/4 or 1/2 note, 500 to 1000 ms at 120 BPM — because the next event is always close. Rock and country ballads commonly sit at a bar, 2000 ms at 120 BPM. Slow ballads, ambient and shoegaze stretch to 2 bars and beyond; at a genuinely slow tempo like 100 BPM that can mean a 4725 ms decay, as in the worked example, without any overlap at all. The warning runs the other way too: a 2-bar preset copied from a slow song into a 150 BPM track compresses to 3200 ms of total, but the arrangement has also sped up, so check it against the next hit rather than trusting the preset name.
One tail per density, not per track
A practical pattern is two decays for a whole mix: a short one (a 1/4 or 1/2 note total) for rhythmic sources that must stay precise, and a long one (a bar or more) reserved for the one or two featured sources the song is actually about. Everything else shares those two, which keeps the imaginary space coherent. For a printable overview of totals at many tempos, the BPM to milliseconds chart for studio reference shows the totals this page subtracts from.
Limitations
A decay that ends on the grid is tidy, not automatically right: in a very sparse arrangement a tail that stops exactly on a bar line can feel artificially cut, and letting it overhang by ear is a legitimate choice. This framework also assumes a steady tempo and a regular meter — in 3/4, 6/8 or rubato material, measure the real gap to the next event in milliseconds and use that as your total instead of a note value. And decay time alone says nothing about tone: a bright 1968.75 ms tail will feel longer than a dark one of the same length, because high-frequency energy stays audible further into the decay. Use the number to place the ending, then use EQ and level to decide how present the journey there should be.
Frequently asked questions
What is the difference between decay time and total reverb time?
Total time runs from the moment the source plays to the moment the reverb is finished. Decay time starts later, after the pre-delay gap, and ends at that same finish point. They are related by one subtraction: decay equals total minus pre-delay, so a 2000 ms total behind a 31.25 ms gap has a decay of 1968.75 ms.
Are decay time, reverb tail and reverb length the same thing?
On this site, yes — all three phrases describe the audible wash after the pre-delay, and this one calculator serves all of them. Manufacturers are less consistent: some label the main knob with the total including the gap, some without. Comparing both numbers from this page against your plugin manual settles which convention yours follows.
How long should a reverb tail be?
As long as the gap before the next important event, and no longer, is the reliable starting rule. At 120 BPM that means about 968.75 ms of decay for a half-note total on rhythmic parts, or 1968.75 ms for a full-bar total on featured parts. Sparse, slow songs can support far longer; dense, fast ones usually cannot.
What decay do I get at 100 BPM for a hall sound?
The Hall total is 2 bars. At 100 BPM a quarter note is 600 ms, so the total is 4800 ms, and after the standard 75 ms pre-delay (a 1/32 note at that tempo) the decay is 4725 ms. It sounds enormous as a raw number, yet it still ends exactly on the bar line because the tempo is slow.
Why does my preset sound shorter in a faster song?
If the preset stores a fixed millisecond decay, it does not change at all — but the music around it moves faster, so the tail overlaps more events and is usually turned down or masked sooner, which reads as shorter. Tempo-derived totals avoid the opposite trap of a slow-song preset flooding a fast track. Recalculate per song rather than trusting preset names.
- Wikipedia — Reverberation — Definitions of reverberation and decay, including the convention of measuring a tail to near-inaudibility.
- iZotope — Learn — Mixing guidance on choosing tail lengths that support rather than obscure an arrangement.
- Sound on Sound — Technique coverage on fitting reverb decay to tempo, density and genre.