psd amplitude scaling

If one creates a 1V RMS sine wave, e.g. with a peak value of 1.414 or

peak-peak of 2.83, then computes psd, the resulting amplitude is around

24 dB, yet classic theory dictates the answer ought to be 20 log(1) = 0

This offset seems consistent across various frequencies/sample

Can someone illuminate the amplitude scaling of the psd algorithm?