# Z:#Neutrons Ratio

Is there a fixed ratio that can be used to calculate the number of neutrons in the nucleus of the most stable isotope of an element by knowing the atomic number?

Side question: if Z is the symbol for atomic number, are there symbols for the number of neutrons and/or atomic mass?

The symbols $Z$, $N$, and $A$ are typically used to describe a nucleus:
$Z$ : atomic number (= number of protons)
$N$ : neutron number
$A$ : mass number ($A = Z + N$)
There is no fixed $Z:N$ ratio throughout the whole periodic table for stable isotopes, but a belt of stability in the Chart of Nuclides.