I am pretty sure that compression is normally recorded in PSI so there should not be any conversion unless its some sort of dynamic compression ratio but I doubt anything would change.
kPa are kilopascals. Normal atmospheric pressure is 14.7psi, or 101.3 kPa or 1 Bar(14.5psi techically). It is all the same thing just using a different unit.
Perhaps you have some very tight rings that seal very well. Would probably give you a high compression ratio in total.
From Wiki
b = cylinder bore (diameter)
s = piston stroke length
Vc = clearance volume. It is the volume of the combustion chamber (including head gasket). This is the minimum volume of the space at the end of the compression stroke, i.e. when the piston reaches top dead center (TDC). Because of the complex shape of this space, it is usually measured directly rather than calculated.