fft - Power Spectrum in dBFs

I'm trying to get the spectrum of my signal in dBFS units. I'm not sure what is the refernce that I should devide by. I computed the power spectrum as follows:

1) FFT normalized to the number of samples

p = abs(fft(signal))/(No_of_samps/2);

2) and then I calculated the power spectrum for half of the samples (one-sided)

p = p(1:Nsamps/2).^2;

3) I tried to represent it in dBFS as follows:

p_dBFs = 10*log(abs(p)/(vref/2)^2);

Where vref is my reference p-p voltage in the ADC.

I'm just not sure whether I should devide by the reference voltage to get values in dBFS, like when I apply a FS signal I would like to see the highest peak in the spectrum at exactly 0 dBFs.

Note: The time-domain signal is also multiplied by a hamming window before computing the FFT.

Any help is appreciated.

Sorry for the long post. Thank you guys very much.