What this calculates
One beat is 60,000 milliseconds divided by the tempo. Every other figure comes off that: a subdivision divides the beat, a dotted value multiplies it by 1.5, a triplet divides it by 1.5, and a passage length is bars times beats times the beat.
Why milliseconds
Delay and modulation are set in milliseconds on most equipment, while music is counted in beats. The conversion is the whole job, and doing it by hand mid-session is where the mistakes come from.
What this cannot judge
Whether a delay time sounds right is not arithmetic. Feel, swing and the character of the room all sit outside these numbers, and plenty of good settings are deliberately off the grid. This gets you to the grid; whether you stay on it is a musical decision.
Common questions
What is a dotted eighth delay in milliseconds?
Set the tempo and read the dotted figure, which is one beat multiplied by 1.5. For an eighth-note version, halve it. The tool shows the beat value alongside so the arithmetic stays visible rather than hidden.
Does this handle odd time signatures?
Yes, for length. Beats per bar is an input, so a bar of five or seven counts as readily as four. Subdivision is independent of the signature.
Why does my delay still sound off?
Timing set from a tempo assumes the performance sits on that tempo. Live playing drifts, and a delay locked to the grid can fight it. That is a musical judgement, not a maths one.