The SNDR can be calculated by the calculator in spectreRF. For the SNR, you need to exclude the distortion products shown in the spectrum. Remember, it is not the distance from signal peak to noise floor -- this distance is usually called SFDR (spurious free dynamic range). Only knowing the noise floor is not sufficient, you also need to know how many FFT points are within your signal-bandwidth and multiply the noise floor (convert back to absolute number, not DB) by the number of in-band FFT points.