Buffer size and sample rate together decide how long it takes a sound to get through your interface and back. Enter the settings your software is actually using and this turns them into milliseconds, and into the distance sound would travel in that time — which is the honest way to judge whether it matters.
The calculator
You enter the settings. Nothing here recommends a buffer size or claims a latency is acceptable, because that depends on what you are playing and how you are monitoring it.
Why the round trip is roughly double
A buffer is filled before it is processed, and the result is filled into another buffer before it is played. Recording and monitoring through software therefore costs you the buffer period at least twice, plus whatever fixed conversion delay the hardware adds — that last figure is the one your interface reports and this page asks for rather than assumes.
The distance comparison
Converting the delay into a distance is the most useful sanity check available, because it turns an abstract number into something you have physically experienced. Standing a few metres from an amp already costs you several milliseconds and nobody finds it disturbing. Enter the speed of sound for your conditions — it changes with temperature and humidity, so the figure is yours to supply.
What it does not do
It does not know about plugin delay compensation, driver overhead, or the extra buffering some software adds on top. Treat the result as the floor rather than the total, and compare it against what your software reports.