Converting from frequency bins to HZ

Hi everyone, I have a frequency vector with range 0:fs/N:fs/2, is this already in Hz or do I still need to multiply it by fs/N. Also I have a plot of the PSD of an EEG signal. I want the y-axis to be in dB/Hz. How do I do this.

[MeitiLuk]

can u maybe show your code?

[Walter Roberson]

That vector is already in Hz.

[Temisanren Okotie]

This is the code

load Subject00_before_fp1.mat;
Sub0 = Subject00_before_fp1(1:5000);
N = length(Sub0);
fs = 500;
t = (1:N)/fs;
subplot(2,1,1);
plot(t,Sub0);
nw = 50;
fp = 0.1;
fst = 25;
wp = fp/fs/2;
ws = fst/fs/2;
wn = [wp,ws];
window = kaiser(nw+1);
b = fir1(nw,wn,'bandpass',window);
y = filter(b,1,Sub0);
subplot(2,1,2);
plot(t,y,'k');
figure;
P = nextpow2(N);
n = 2^P;
X = fft(y,n);
X = X(1:N/2+1);
Pxx = (1/(fs*N)) * abs(X).^2;
Pxx(2:end-1) = 2*Pxx(2:end-1);
f = (0:fs/N:fs/2)*fs/N;
plot(f,10*log10(Pxx));

[Ayush Bansal]

The vector is alreay in Hz. 0:fs/N:fs/2 will create a vector from 0 to fs/2 with increment of fs/N Hz. Use pwelch(x) for PSD of a signal.