1st you need at least one more info, i.e. IP3, more exactly you must define what "type" of IP3: i.e. Two Tone Output IP3 (TTOIP3)
2nd:
The ratio between MDS and Two Tone signal Level whose Third order IM products are equal to MDS (then may be transformed in dB... 10 log...)
MDS=Minimum discernible signal = K Top B
K= Boltzmann Konstant
Top= Noise operative temperature (Te+Tantenna)
B= Bandwidth
All data on SI units
3rd: download the trial version of SysCalc. It perform calculations fast and it's fiendly.