If m = is in kg, acceleration due to gravity(g) = m/s² and h = meter: the unit of potenial energy PE would be Joules..
Note: 1 Joule = 1 Newton-meter.
1 Newton = 1 kg -m/s²
If we will take a look at the units of the formula for potential energy PE:
we will have this:
PE = mgh
= kg x m/s² x m
PE = Joules(J)