It’s very simple.
RF LOAD = (# of TRX in cell – 1) / (# of hopping frequencies in the cell)
(note : hopping frequencies are not including the BCCH frequency !)
This formula works for any kind of of SFH (1×1 or 1×3)
Now, depending on your SFH type, apply different thresholds :
if SFH 1×1, RF LOAD should be less than 12%. (max theoretical is 16% – but hard to achieve with a serious degradation of qos)
if SFH 1×3, RF load should be less than 30% (max theo is … 50% ? I forgot… anyway, theo limit is just a figure)
Hope it helps 🙂