To determine the noise figure (NF) of a device use the relationship NF= (S/N)in/(S/N)out. Then in order to find the noise temperature use Td = To*(NF - 1) where To is the reference temperature (usually 290 K). The noise figure NF is given in dB but this app converts it to a linear ratio.

As an example, enter To = 290, NF = 2.5, push "Calculate" and your result should be Td = 225.7.