How to calculate fft bin size

i am using this code for mel frequency spectrum calculation, but i dont know how to calculate fft bin value?? what formula exactly use here in following code.

function z = melfspectrum(nMelf, nFFT, fs, data) %#codegen % MELFSPECTRUM Calculate Mel-frequency spectrum of frammed audio data % % Inputs: nMelf number of filters in filterbank % nFFT length of fft % fs sample rate in Hz % % Outputs: z the Mel-frequency spectrum % nFFT = 256; nMelf = 16;

%% Generate a bank of Mel-filter f0 = 700 / 22050; fn2 = floor(nFFT/2);

lr = log(1 + 0.5/f0) / (nMelf+1);

% convert to fft bin numbers with 0 for DC term bl = nFFT * (f0 * (exp([0 1 nMelf nMelf+1] * lr) - 1));

b1 = floor(bl(1)) + 1; b2 = ceil(bl(2)); b3 = floor(bl(3)); b4 = min(fn2, ceil(bl(4))) - 1;

pf = log(1 + (b1:b4)/nFFT/f0) / lr; %%%%% frequency to mel conversion fp = floor(pf); pm = pf - fp;

r = [fp(b2:b4) 1+fp(1:b3)]; c = [b2:b4 1:b3] + 1; v = 2 * [1-pm(b2:b4) pm(1:b3)];

%% Calculating Mel-frequency spectrum % by applying the Mel-filters to the spectrum of audio data % implement product of sparse matrices

data_Frq=framedFFT(1:1+fn2, :).^2; [nRow,nCol]=size(data_Frq); z=zeros(nMelf,nCol); for k=1:nCol for i=1:nMelf ind=find(r==i); c_ithrow=c(ind); f_ithrow=v(ind); z(i,k)=f_ithrow*data_Frq(c_ithrow,k); end; end; % for double check the implementation of sparse matric % m = sparse(r, c, v, nMelf, 1+fn2); % z0 = m * data(1:1+fn2, :).^2;