FFT and SPL: Calibrating a microphone?

I’m trying to calibrate a microphone for further measurements. I have this equipment: - Microphone Sensitivity: 50mV/Pa - Preamp and A/D Converter gain: 0dB And I want to calibrate it using: - Bruel 4231 Calibrator 94dB @ 1Khz.

So I wrote the following program to analyze the calibrator signal:

Pref=20e-6;
MIC_gain=50e-3;%50mV/pA
%VarName1 manually imported: Time
%VarName3 manually imported: Volts
N=length(VarName1);
fs=1/(VarName1(2)-VarName1(1));
VarName3=VarName3./MIC_gain;
RMS = sqrt(mean(VarName3.^2));

% Just for information - not used
DbTOTAL=20*log10(RMS/Pref);
% Flat top windowing
VarName3=VarName3.*flattopwin(N)';
% DFT
y=fft(VarName3); 
% dB - Is it OK?
db = 20*log10((2/N).*(RMS).*(abs(y)/Pref));

f = (0:length(VarName1)-1)*fs/length(VarName1);
figure
% Still have to cut freq up to Fs/2
plot(f,db);

My idea is to measure the higher peak at around 1Khz and compare it with 94db, to get a calibration constant. Any advice/correction is welcome. Thanks!