Kinetic inductance detectors are based upon high Q superconducting resonators. We have measured the electrical Noise Equivalent Power (NEP) of 100 nm thick 1/4 λ coplanar waveguide Aluminum resonators at 100 mK using phase readout and radius readout. We find that the phase NEP is independent of the Q factor of the resonator, limited by excess noise in the KID and given by NEP {}=9× 10^{-18} W/sqrt{Hz} at 100 Hz. It increases with roughly f -0.5 at lower frequencies. The amplitude NEP is strongly Q factor dependent, limited by the setup noise, nearly frequency independent and as low as NEP {}=3×10^{-18} W/sqrt{Hz} for a high Q resonator (Q=454.000). For lower Q resonators the amplitude NEP increases to values equal to or even larger than the phase readout.
