You can use arbitrary values of
In arbitrary units, the Pauling scale:
Nonpolar covalent bonds when,
Polar covalent bonds when,
Ionic bonds when,
Of course, you need some sort of chart or table to do this (mainly the Pauling scale values), but if you do not have a chart with electronegativity values to compare, consider this:
If the compound is ionic (metal + nonmetal constituents) the bond formed will be ionic.
If the compound is molecular, the bond formed could be a polar covalent bond or a nonpolar covalent bond depending on "close" the bonded species are on the periodic table.
As expected then, for diatomics, the bond is formed is nonpolar covalent. Such as
But, the bond between two molecular species can sometimes be ionic, in the case of
You can find elctronegavity values here: