low frequency signal power spectrum density with fft or pwelch. too high magnitude

Hello, I am trying to get the psd result of a low frequency signal. And the pwelch picks the correct frequency but the magnitude is much bigger than it is supposed to be. Have a look at the code and the psd result.

fs=10; % Hz
t=0:1/fs:10800;  % sec
L=length(t);
NFFT=L;
x=1*cos(2*pi*0.01*t) +2*cos(2*pi*0.3*t)+ 0.5*cos(2*pi*0.0015*t);
[sp,ff] = pwelch(x,NFFT,[],NFFT,fs,'onesided','psd');

Answer 1

[Abhishek Ballaney]

https://in.mathworks.com/help/signal/ref/pwelch.html

[MINSOO KIM]

Thanks but I read through the matlab help. I could not find any clue.